diff --git a/apps/_shared/vite-public-app.mjs b/apps/_shared/vite-public-app.mjs
index a7bc0b59378..d34a3d4c017 100644
--- a/apps/_shared/vite-public-app.mjs
+++ b/apps/_shared/vite-public-app.mjs
@@ -5,13 +5,15 @@
  *
  * Each app loads as a <script src> from a Ghost theme and ships as a UMD
  * (or IIFE) bundle in <app>/umd/<app>.min.js. This factory captures the
- * shape they all share (outDir, lib, optional i18n locale glob, baseline
- * plugins) and lets per-app divergence flow through `overrides`, which is
- * deep-merged via Vite's `mergeConfig`. Plugin arrays in `overrides` are
- * appended to the base plugins.
+ * shape they all share (outDir, lib, baseline plugins) and lets per-app
+ * divergence flow through `overrides`, which is deep-merged via Vite's
+ * `mergeConfig`. Plugin arrays in `overrides` are appended to the base plugins.
  *
  * Plugin imports are dynamic so an app can opt out (e.g. admin-toolbar
  * uses Preact and never installs `@vitejs/plugin-react`).
+ *
+ * i18n note: apps import their locales via `@tryghost/i18n/registry/<namespace>`,
+ * a static ESM registry any bundler can resolve.
  */
 import {resolve} from 'path';
 import {defineConfig, mergeConfig} from 'vitest/config';
@@ -27,7 +29,6 @@ import {defineConfig, mergeConfig} from 'vitest/config';
  * @param {string} [opts.libName] — global var name override (default: `packageName`)
  * @param {boolean} [opts.sourcemap=true]
  * @param {boolean} [opts.cssCodeSplit=true]
- * @param {string} [opts.i18nNamespace] — if set, wires `commonjsOptions` to glob `ghost/i18n/locales/*\/<ns>.json`
  * @param {import('vitest/config').UserConfig} [opts.overrides] — deep-merged onto the base config
  * @returns {import('vitest/config').UserConfig}
  */
@@ -42,7 +43,6 @@ export function publicAppViteConfig(opts) {
         libName,
         sourcemap = true,
         cssCodeSplit = true,
-        i18nNamespace,
         overrides = {}
     } = opts;
 
@@ -80,18 +80,7 @@ export function publicAppViteConfig(opts) {
                     formats: [libFormat],
                     name: libName ?? packageName,
                     fileName: () => `${outputFileName}.min.js`
-                },
-                ...(i18nNamespace && {
-                    commonjsOptions: {
-                        include: [/ghost/, /node_modules/],
-                        dynamicRequireRoot: '../../',
-                        // Single glob expands to all SUPPORTED_LOCALES; passing each
-                        // locale as an explicit path triggers a full repo-root
-                        // directory crawl per entry under vite 7's bundled
-                        // @rollup/plugin-commonjs, adding ~1s per locale to build time.
-                        dynamicRequireTargets: [`../../ghost/i18n/locales/*/${i18nNamespace}.json`]
-                    }
-                })
+                }
             },
             test: {
                 globals: true,
diff --git a/apps/comments-ui/src/app.tsx b/apps/comments-ui/src/app.tsx
index d0acb42041e..9e4d2d416a8 100644
--- a/apps/comments-ui/src/app.tsx
+++ b/apps/comments-ui/src/app.tsx
@@ -4,7 +4,7 @@ import AuthFrame from './auth-frame';
 import ContentBox from './components/content-box';
 import PopupBox from './components/popup-box';
 import React, {useCallback, useEffect, useMemo, useState} from 'react';
-import i18nLib from '@tryghost/i18n';
+import i18nLib from '@tryghost/i18n/registry/comments';
 import setupGhostApi from './utils/api';
 import {ActionHandler, SyncActionHandler, isSyncAction} from './actions';
 import {AppContext, Comment, DispatchActionType, EditableAppContext} from './app-context';
diff --git a/apps/comments-ui/test/unit/components/content/pagination.test.jsx b/apps/comments-ui/test/unit/components/content/pagination.test.jsx
index 443479e7b4e..1a78d220f42 100644
--- a/apps/comments-ui/test/unit/components/content/pagination.test.jsx
+++ b/apps/comments-ui/test/unit/components/content/pagination.test.jsx
@@ -1,5 +1,5 @@
 import Pagination from '../../../../src/components/content/pagination';
-import i18nLib from '@tryghost/i18n';
+import i18nLib from '@tryghost/i18n/registry/comments';
 import {AppContext} from '../../../../src/app-context';
 import {render, screen} from '@testing-library/react';
 
diff --git a/apps/comments-ui/vite.config.mts b/apps/comments-ui/vite.config.mts
index 5243ff901ed..19064ded2c2 100644
--- a/apps/comments-ui/vite.config.mts
+++ b/apps/comments-ui/vite.config.mts
@@ -7,7 +7,6 @@ export default publicAppViteConfig({
     packageRoot: import.meta.dirname,
     packageName: pkg.name,
     entry: 'src/index.tsx',
-    i18nNamespace: 'comments',
     sourcemap: false,
     overrides: {
         plugins: [stripFingerprintingPlugin()],
diff --git a/apps/portal/src/utils/i18n.js b/apps/portal/src/utils/i18n.js
index ae67868b13f..dc0ff6cf5cb 100644
--- a/apps/portal/src/utils/i18n.js
+++ b/apps/portal/src/utils/i18n.js
@@ -1,4 +1,4 @@
-import i18nLib from '@tryghost/i18n';
+import i18nLib from '@tryghost/i18n/registry/portal';
 
 const i18n = i18nLib('en', 'portal');
 
diff --git a/apps/portal/test/errors.test.js b/apps/portal/test/errors.test.js
index ffa8eec93fd..c947ff66210 100644
--- a/apps/portal/test/errors.test.js
+++ b/apps/portal/test/errors.test.js
@@ -1,7 +1,7 @@
 import {HumanReadableError, chooseBestErrorMessage} from '../src/utils/errors';
 import {vi} from 'vitest';
 
-vi.mock('@tryghost/i18n', () => {
+vi.mock('@tryghost/i18n/registry/portal', () => {
     const mockT = vi.fn((message, params) => {
         if (params?.number) {
             return `translated ${message.replace('{number}', params.number)}`;
diff --git a/apps/portal/test/utils/test-utils.jsx b/apps/portal/test/utils/test-utils.jsx
index 8b1cba5ad75..04330fd9da8 100644
--- a/apps/portal/test/utils/test-utils.jsx
+++ b/apps/portal/test/utils/test-utils.jsx
@@ -1,6 +1,6 @@
 // Common test setup util - Ref: https://testing-library.com/docs/react-testing-library/setup#custom-render
 import {render} from '@testing-library/react';
-import i18n from '@tryghost/i18n';
+import i18n from '@tryghost/i18n/registry/portal';
 import AppContext from '../../src/app-context';
 import {testSite, member} from '../../src/utils/fixtures';
 
diff --git a/apps/portal/vite.config.mjs b/apps/portal/vite.config.mjs
index f7cb4d52b0a..1c257926078 100644
--- a/apps/portal/vite.config.mjs
+++ b/apps/portal/vite.config.mjs
@@ -6,7 +6,6 @@ export default publicAppViteConfig({
     packageRoot: import.meta.dirname,
     packageName: pkg.name,
     entry: 'src/index.jsx',
-    i18nNamespace: 'portal',
     cssCodeSplit: false,
     overrides: {
         define: {
diff --git a/apps/signup-form/.storybook/preview.tsx b/apps/signup-form/.storybook/preview.tsx
index 5ad0def51e0..56268773ab7 100644
--- a/apps/signup-form/.storybook/preview.tsx
+++ b/apps/signup-form/.storybook/preview.tsx
@@ -1,4 +1,4 @@
-import * as i18nLibModule from '@tryghost/i18n';
+import * as i18nLibModule from '@tryghost/i18n/registry/signup-form';
 import React from 'react';
 
 import type {Preview} from "@storybook/react-vite";
diff --git a/apps/signup-form/src/app.tsx b/apps/signup-form/src/app.tsx
index a7701809a2c..285990af919 100644
--- a/apps/signup-form/src/app.tsx
+++ b/apps/signup-form/src/app.tsx
@@ -1,4 +1,4 @@
-import * as i18nLibModule from '@tryghost/i18n';
+import * as i18nLibModule from '@tryghost/i18n/registry/signup-form';
 import React, {ComponentProps} from 'react';
 import pages, {Page, PageName} from './pages';
 import {AppContextProvider, AppContextType} from './app-context';
diff --git a/apps/signup-form/src/i18n.d.ts b/apps/signup-form/src/i18n.d.ts
index 36ee2a9b25b..78c1aeec16d 100644
--- a/apps/signup-form/src/i18n.d.ts
+++ b/apps/signup-form/src/i18n.d.ts
@@ -1 +1,2 @@
 declare module '@tryghost/i18n';
+declare module '@tryghost/i18n/registry/signup-form';
diff --git a/apps/signup-form/src/preview.stories.tsx b/apps/signup-form/src/preview.stories.tsx
index 39c6849a349..94c7d48f57b 100644
--- a/apps/signup-form/src/preview.stories.tsx
+++ b/apps/signup-form/src/preview.stories.tsx
@@ -1,4 +1,4 @@
-import * as i18nLibModule from '@tryghost/i18n';
+import * as i18nLibModule from '@tryghost/i18n/registry/signup-form';
 import React, {useState} from 'react';
 import pages, {Page, PageName} from './pages';
 import {AppContextProvider, SignupFormOptions} from './app-context';
diff --git a/apps/signup-form/vite.config.mts b/apps/signup-form/vite.config.mts
index 9b2852bfa9a..07087540c35 100644
--- a/apps/signup-form/vite.config.mts
+++ b/apps/signup-form/vite.config.mts
@@ -5,7 +5,6 @@ export default publicAppViteConfig({
     packageRoot: import.meta.dirname,
     packageName: pkg.name,
     entry: 'src/index.tsx',
-    i18nNamespace: 'signup-form',
     sourcemap: false,
     overrides: {
         define: {
diff --git a/apps/sodo-search/src/app.jsx b/apps/sodo-search/src/app.jsx
index 85949f5d639..13cbe38b10a 100644
--- a/apps/sodo-search/src/app.jsx
+++ b/apps/sodo-search/src/app.jsx
@@ -2,7 +2,7 @@ import AppContext from './app-context';
 import PopupModal from './components/popup-modal';
 import React from 'react';
 import SearchIndex from './search-index.js';
-import i18nLib from '@tryghost/i18n';
+import i18nLib from '@tryghost/i18n/registry/search';
 
 export default class App extends React.Component {
     constructor(props) {
diff --git a/apps/sodo-search/vite.config.mjs b/apps/sodo-search/vite.config.mjs
index 8037276cf7c..9cde3ff2e3a 100644
--- a/apps/sodo-search/vite.config.mjs
+++ b/apps/sodo-search/vite.config.mjs
@@ -6,7 +6,6 @@ export default publicAppViteConfig({
     packageRoot: import.meta.dirname,
     packageName: pkg.name,
     entry: 'src/index.jsx',
-    i18nNamespace: 'search',
     sourcemap: false,
     cssCodeSplit: false,
     overrides: {
diff --git a/ghost/i18n/eslint.config.mjs b/ghost/i18n/eslint.config.mjs
index 9f9e5f56992..aa89a90c691 100644
--- a/ghost/i18n/eslint.config.mjs
+++ b/ghost/i18n/eslint.config.mjs
@@ -1,6 +1,10 @@
 import {nodeLibConfig, noGhostIgnitionRequireRule} from '../../eslint.shared.mjs';
 
-export default await nodeLibConfig({
+export default [{
+    // Generated locale registries and ESM entry glue are code-generated / hand-authored
+    // ESM shims; they're not part of the linted CJS source surface.
+    ignores: ['lib/registry/**', 'build/**']
+}, ...await nodeLibConfig({
     // ghost/i18n is JS-only (CommonJS) and uses the local-filenames variant of
     // match-regex instead of the ghost-plugin one. legacyLocalFilenames handles both.
     typescript: false,
@@ -25,6 +29,17 @@ export default await nodeLibConfig({
             // Keep the index entry points small — they're public surface.
             files: ['lib/**/index.js', 'index.js'],
             rules: {'max-lines': ['error', {skipBlankLines: true, skipComments: true, max: 50}]}
+        },
+        {
+            // Hand-authored ESM entry glue (lib/esm-factory.mjs). Lint it as real ESM so
+            // it isn't silently rule-less. The generated lib/registry/** stays ignored.
+            files: ['*.mjs', 'lib/**/*.mjs'],
+            languageOptions: {sourceType: 'module'},
+            rules: {
+                'no-unused-vars': 'error',
+                'no-undef': 'error'
+            }
         }
     ]
-});
+})];
+
diff --git a/ghost/i18n/index.browser.js b/ghost/i18n/index.browser.js
deleted file mode 100644
index d841af384a9..00000000000
--- a/ghost/i18n/index.browser.js
+++ /dev/null
@@ -1,8 +0,0 @@
-const i18n = require('./lib/i18n.browser');
-
-// Explicit exports for better bundler compatibility
-module.exports = i18n;
-module.exports.default = i18n;
-module.exports.LOCALE_DATA = i18n.LOCALE_DATA;
-module.exports.SUPPORTED_LOCALES = i18n.SUPPORTED_LOCALES;
-module.exports.generateResources = i18n.generateResources;
diff --git a/ghost/i18n/index.d.ts b/ghost/i18n/index.d.ts
new file mode 100644
index 00000000000..f69361bd5d3
--- /dev/null
+++ b/ghost/i18n/index.d.ts
@@ -0,0 +1,27 @@
+import type {i18n as I18nextInstance} from 'i18next';
+
+export interface LocaleDataEntry {
+    code: string;
+    name: string;
+    [key: string]: unknown;
+}
+
+export type Namespace = 'ghost' | 'portal' | 'signup-form' | 'comments' | 'search' | 'theme';
+
+export interface I18nFactory {
+    (locale?: string, ns?: Namespace | string, options?: Record<string, unknown>): I18nextInstance;
+    LOCALE_DATA: LocaleDataEntry[];
+    SUPPORTED_LOCALES: string[];
+    generateResources(locales: string[], ns: string): Record<string, Record<string, Record<string, string>>>;
+    default: I18nFactory;
+}
+
+declare const i18n: I18nFactory;
+
+export default i18n;
+export declare const LOCALE_DATA: LocaleDataEntry[];
+export declare const SUPPORTED_LOCALES: string[];
+export declare function generateResources(
+    locales: string[],
+    ns: string
+): Record<string, Record<string, Record<string, string>>>;
diff --git a/ghost/i18n/lib/esm-factory.mjs b/ghost/i18n/lib/esm-factory.mjs
new file mode 100644
index 00000000000..fe15dd18a33
--- /dev/null
+++ b/ghost/i18n/lib/esm-factory.mjs
@@ -0,0 +1,63 @@
+/**
+ * Shared ESM factory for the browser/static-registry build.
+ *
+ * Given a single-namespace registry (locale-code -> resource JSON), returns an
+ * i18n factory with the SAME call signature the CJS package exposes:
+ *   i18n(locale, ns, options) -> initialised i18next instance
+ *
+ * Theme resources are stubbed to `{}` — themes are a Node-only, fs-backed concept
+ * and never reach the browser (matches the old index.browser.js).
+ *
+ * The namespace is fixed at build time by which per-namespace registry module is
+ * imported, so bundlers include ONLY that namespace's locale files.
+ *
+ * Note: this imports the ESM core (./i18n-core.mjs), NOT the CJS ./i18n-core.js.
+ * The CJS core uses require('i18next'), which leaks a bare `require(...)` into the
+ * browser UMD bundle and throws "require is not defined" at load.
+ */
+import * as i18nCore from './i18n-core.mjs';
+
+const {createI18n, createGenerateResources, LOCALE_DATA, SUPPORTED_LOCALES} = i18nCore;
+
+/**
+ * Shared body of every per-namespace browser entry. Collects a Vite
+ * `import.meta.glob` result (path -> resource JSON) into a locale-keyed registry
+ * and builds the namespaced i18n instance.
+ *
+ * This exists because Vite requires the `import.meta.glob` pattern to be a string
+ * literal, so each namespace needs its own tiny entry to hold that literal — but
+ * the parsing/wiring is identical, so it lives here once.
+ */
+export function i18nFromGlob(globModules, namespace) {
+    const registry = {};
+    for (const [filePath, resource] of Object.entries(globModules)) {
+        registry[filePath.match(/\/locales\/([^/]+)\//)[1]] = resource;
+    }
+    return createNamespacedI18n(registry, namespace);
+}
+
+export function createNamespacedI18n(registry, boundNamespace) {
+    // Registry loader: returns undefined for an unknown locale so the core falls
+    // back to English (mirrors the CJS try/catch fallback).
+    const generateResources = createGenerateResources(locale => registry[locale]);
+
+    function generateThemeResources(lng) {
+        return {
+            [lng]: {
+                theme: {}
+            }
+        };
+    }
+
+    const i18n = createI18n({generateResources, generateThemeResources});
+
+    i18n.LOCALE_DATA = LOCALE_DATA;
+    i18n.SUPPORTED_LOCALES = SUPPORTED_LOCALES;
+    i18n.generateResources = generateResources;
+    i18n.namespace = boundNamespace;
+    i18n.default = i18n;
+
+    return i18n;
+}
+
+export {LOCALE_DATA, SUPPORTED_LOCALES};
diff --git a/ghost/i18n/lib/i18n-core.js b/ghost/i18n/lib/i18n-core.js
index 909875e13e2..ff2784b1de9 100644
--- a/ghost/i18n/lib/i18n-core.js
+++ b/ghost/i18n/lib/i18n-core.js
@@ -1,3 +1,11 @@
+// CJS (Node) core for @tryghost/i18n.
+//
+// Sibling of ./i18n-core.mjs (the ESM/browser twin). Ghost core require()s this
+// package synchronously, so the Node path must stay CommonJS; the browser path
+// must be pure ESM (a CJS file in the browser bundle leaks a bare `require(...)`
+// or `module.exports` and throws at load). The two cores are therefore kept as
+// deliberate twins and guarded by a parity test in test/i18n.test.js — change
+// shared behaviour in BOTH files.
 const i18next = require('i18next');
 
 // Locale data loaded from JSON (single source of truth)
@@ -6,27 +14,36 @@ const LOCALE_DATA = require('./locale-data.json');
 // Export just the locale codes for backward compatibility
 const SUPPORTED_LOCALES = LOCALE_DATA.map(locale => locale.code);
 
-function generateResources(locales, ns) {
-    return locales.reduce((acc, locale) => {
-        let res;
-        // add an extra fallback - this handles the case where we have a partial set of translations for some reason
-        // by falling back to the english translations
-        try {
-            res = require(`../locales/${locale}/${ns}.json`);
-        } catch (err) {
-            res = require(`../locales/en/${ns}.json`);
-        }
+// Merge quirk preserved verbatim from the original implementation:
+// Note: due some random thing in TypeScript, 'requiring' a JSON file with a space in a key name, only adds it to the default export
+// If changing this behaviour, please also check the comments and signup-form apps in another language (mainly sentences with a space in them)
+function mergeDefaultExport(res) {
+    return {...res, ...(res.default && typeof res.default === 'object' ? res.default : {})};
+}
 
-        // Note: due some random thing in TypeScript, 'requiring' a JSON file with a space in a key name, only adds it to the default export
-        // If changing this behaviour, please also check the comments and signup-form apps in another language (mainly sentences with a space in them)
-        acc[locale] = {
-            [ns]: {...res, ...(res.default && typeof res.default === 'object' ? res.default : {})}
-        };
-        return acc;
-    }, {});
+// Factory: given a resource loader, produce a `generateResources(locales, ns)` fn
+// with the exact original behaviour/shape. Callers that need the classic dynamic-require
+// behaviour just use the default-exported `generateResources` below.
+function createGenerateResources(loadResource) {
+    return function generateResources(locales, ns) {
+        return locales.reduce((acc, locale) => {
+            let res = loadResource(locale, ns);
+            // Fallback to English if a locale/namespace pair is missing entirely.
+            if (res === undefined) {
+                res = loadResource('en', ns);
+            }
+            // English floor: if even English is missing for this namespace, use an
+            // empty object so the promised English fallback never lets
+            // mergeDefaultExport receive undefined (which would throw).
+            acc[locale] = {
+                [ns]: mergeDefaultExport(res || {})
+            };
+            return acc;
+        }, {});
+    };
 }
 
-function createI18n({generateThemeResources}) {
+function createI18n({generateThemeResources, generateResources: genResources}) {
     return (lng = 'en', ns = 'portal', options = {}) => {
         const i18nextInstance = i18next.createInstance();
         const interpolation = {
@@ -38,7 +55,7 @@ function createI18n({generateThemeResources}) {
         }
         let resources;
         if (ns !== 'theme') {
-            resources = generateResources(SUPPORTED_LOCALES, ns);
+            resources = genResources(SUPPORTED_LOCALES, ns);
         } else {
             resources = generateThemeResources(lng, options);
         }
@@ -74,7 +91,8 @@ function createI18n({generateThemeResources}) {
 
 module.exports = {
     createI18n,
-    generateResources,
+    createGenerateResources,
+    mergeDefaultExport,
     LOCALE_DATA,
     SUPPORTED_LOCALES
 };
diff --git a/ghost/i18n/lib/i18n-core.mjs b/ghost/i18n/lib/i18n-core.mjs
new file mode 100644
index 00000000000..35cc82c28b4
--- /dev/null
+++ b/ghost/i18n/lib/i18n-core.mjs
@@ -0,0 +1,93 @@
+/**
+ * ESM (browser) core for @tryghost/i18n — the pure-ESM twin of ./i18n-core.js.
+ *
+ * The per-namespace registry entries load through ./esm-factory.mjs, so this
+ * path must stay 100% ESM: a CJS file anywhere in the browser graph leaks a
+ * bare `require(...)` or `module.exports` into the UMD bundle and throws
+ * ("require is not defined" / "module is not defined") at load. That is why the
+ * core is duplicated here rather than shared from the CJS file.
+ *
+ * Keep behaviour identical to ./i18n-core.js — the two are guarded by a parity
+ * test in test/i18n.test.js. Change shared behaviour in BOTH files.
+ */
+import i18next from 'i18next';
+import LOCALE_DATA from './locale-data.json' with {type: 'json'};
+
+// Export just the locale codes for backward compatibility
+const SUPPORTED_LOCALES = LOCALE_DATA.map(locale => locale.code);
+
+// Merge quirk preserved verbatim from the original implementation:
+// Note: due some random thing in TypeScript, 'requiring' a JSON file with a space in a key name, only adds it to the default export
+// If changing this behaviour, please also check the comments and signup-form apps in another language (mainly sentences with a space in them)
+function mergeDefaultExport(res) {
+    return {...res, ...(res.default && typeof res.default === 'object' ? res.default : {})};
+}
+
+// Factory: given a resource loader, produce a `generateResources(locales, ns)` fn
+// with the exact original behaviour/shape.
+function createGenerateResources(loadResource) {
+    return function generateResources(locales, ns) {
+        return locales.reduce((acc, locale) => {
+            let res = loadResource(locale, ns);
+            // Fallback to English if a locale/namespace pair is missing entirely.
+            if (res === undefined) {
+                res = loadResource('en', ns);
+            }
+            // English floor: if even English is missing for this namespace, use an
+            // empty object so the promised English fallback never lets
+            // mergeDefaultExport receive undefined (which would throw).
+            acc[locale] = {
+                [ns]: mergeDefaultExport(res || {})
+            };
+            return acc;
+        }, {});
+    };
+}
+
+function createI18n({generateThemeResources, generateResources: genResources}) {
+    return (lng = 'en', ns = 'portal', options = {}) => {
+        const i18nextInstance = i18next.createInstance();
+        const interpolation = {
+            prefix: '{',
+            suffix: '}'
+        };
+        if (ns === 'theme' || ns === 'portal') {
+            interpolation.escapeValue = false;
+        }
+        let resources;
+        if (ns !== 'theme') {
+            resources = genResources(SUPPORTED_LOCALES, ns);
+        } else {
+            resources = generateThemeResources(lng, options);
+        }
+
+        i18nextInstance.init({
+            lng,
+
+            // allow keys to be phrases having `:`, `.`
+            nsSeparator: false,
+            keySeparator: false,
+
+            // if the value is an empty string, return the key
+            returnEmptyString: false,
+
+            // do not load a fallback
+            fallbackLng: {
+                no: ['nb', 'en'],
+                default: ['en']
+            },
+
+            ns: ns,
+            defaultNS: ns,
+
+            // separators
+            interpolation,
+
+            resources
+        });
+
+        return i18nextInstance;
+    };
+}
+
+export {createI18n, createGenerateResources, mergeDefaultExport, LOCALE_DATA, SUPPORTED_LOCALES};
diff --git a/ghost/i18n/lib/i18n.browser.js b/ghost/i18n/lib/i18n.browser.js
deleted file mode 100644
index 10a558b4c60..00000000000
--- a/ghost/i18n/lib/i18n.browser.js
+++ /dev/null
@@ -1,16 +0,0 @@
-const {createI18n, generateResources, LOCALE_DATA, SUPPORTED_LOCALES} = require('./i18n-core');
-
-function generateThemeResources(lng) {
-    return {
-        [lng]: {
-            theme: {}
-        }
-    };
-}
-
-const i18n = createI18n({generateThemeResources});
-
-module.exports = i18n;
-module.exports.SUPPORTED_LOCALES = SUPPORTED_LOCALES;
-module.exports.LOCALE_DATA = LOCALE_DATA;
-module.exports.generateResources = generateResources;
diff --git a/ghost/i18n/lib/i18n.js b/ghost/i18n/lib/i18n.js
index 96330ca5c85..321dfa22d60 100644
--- a/ghost/i18n/lib/i18n.js
+++ b/ghost/i18n/lib/i18n.js
@@ -1,7 +1,10 @@
 const path = require('path');
 const fs = require('fs');
 const debug = require('@tryghost/debug')('i18n');
-const {createI18n, generateResources, LOCALE_DATA, SUPPORTED_LOCALES} = require('./i18n-core');
+const {createI18n, createGenerateResources, LOCALE_DATA, SUPPORTED_LOCALES} = require('./i18n-core');
+const {requireLoader} = require('./require-loader');
+
+const generateResources = createGenerateResources(requireLoader);
 
 function generateThemeResources(lng, themeLocalesPath) {
     if (!themeLocalesPath) {
@@ -76,6 +79,7 @@ function generateThemeResources(lng, themeLocalesPath) {
 }
 
 const i18n = createI18n({
+    generateResources,
     generateThemeResources(lng, options) {
         debug(`generateThemeResources: ${lng}, ${options.themePath}`);
         return generateThemeResources(lng, options.themePath);
diff --git a/ghost/i18n/lib/registry/comments.mjs b/ghost/i18n/lib/registry/comments.mjs
new file mode 100644
index 00000000000..3ace63a2cea
--- /dev/null
+++ b/ghost/i18n/lib/registry/comments.mjs
@@ -0,0 +1,9 @@
+// Per-namespace browser entry — import as '@tryghost/i18n/registry/comments'.
+// Only the literal glob pattern + namespace name live here (Vite requires the
+// glob to be a string literal); all wiring is in ../esm-factory.mjs.
+import {i18nFromGlob} from '../esm-factory.mjs';
+
+const i18n = i18nFromGlob(import.meta.glob('../../locales/*/comments.json', {eager: true, import: 'default'}), 'comments');
+
+export default i18n;
+export const {LOCALE_DATA, SUPPORTED_LOCALES, generateResources} = i18n;
diff --git a/ghost/i18n/lib/registry/ghost.mjs b/ghost/i18n/lib/registry/ghost.mjs
new file mode 100644
index 00000000000..ba92610c0a8
--- /dev/null
+++ b/ghost/i18n/lib/registry/ghost.mjs
@@ -0,0 +1,9 @@
+// Per-namespace browser entry — import as '@tryghost/i18n/registry/ghost'.
+// Only the literal glob pattern + namespace name live here (Vite requires the
+// glob to be a string literal); all wiring is in ../esm-factory.mjs.
+import {i18nFromGlob} from '../esm-factory.mjs';
+
+const i18n = i18nFromGlob(import.meta.glob('../../locales/*/ghost.json', {eager: true, import: 'default'}), 'ghost');
+
+export default i18n;
+export const {LOCALE_DATA, SUPPORTED_LOCALES, generateResources} = i18n;
diff --git a/ghost/i18n/lib/registry/portal.mjs b/ghost/i18n/lib/registry/portal.mjs
new file mode 100644
index 00000000000..65364f8a3be
--- /dev/null
+++ b/ghost/i18n/lib/registry/portal.mjs
@@ -0,0 +1,9 @@
+// Per-namespace browser entry — import as '@tryghost/i18n/registry/portal'.
+// Only the literal glob pattern + namespace name live here (Vite requires the
+// glob to be a string literal); all wiring is in ../esm-factory.mjs.
+import {i18nFromGlob} from '../esm-factory.mjs';
+
+const i18n = i18nFromGlob(import.meta.glob('../../locales/*/portal.json', {eager: true, import: 'default'}), 'portal');
+
+export default i18n;
+export const {LOCALE_DATA, SUPPORTED_LOCALES, generateResources} = i18n;
diff --git a/ghost/i18n/lib/registry/search.mjs b/ghost/i18n/lib/registry/search.mjs
new file mode 100644
index 00000000000..c5a82c1ff57
--- /dev/null
+++ b/ghost/i18n/lib/registry/search.mjs
@@ -0,0 +1,9 @@
+// Per-namespace browser entry — import as '@tryghost/i18n/registry/search'.
+// Only the literal glob pattern + namespace name live here (Vite requires the
+// glob to be a string literal); all wiring is in ../esm-factory.mjs.
+import {i18nFromGlob} from '../esm-factory.mjs';
+
+const i18n = i18nFromGlob(import.meta.glob('../../locales/*/search.json', {eager: true, import: 'default'}), 'search');
+
+export default i18n;
+export const {LOCALE_DATA, SUPPORTED_LOCALES, generateResources} = i18n;
diff --git a/ghost/i18n/lib/registry/signup-form.mjs b/ghost/i18n/lib/registry/signup-form.mjs
new file mode 100644
index 00000000000..69b04d9c81e
--- /dev/null
+++ b/ghost/i18n/lib/registry/signup-form.mjs
@@ -0,0 +1,9 @@
+// Per-namespace browser entry — import as '@tryghost/i18n/registry/signup-form'.
+// Only the literal glob pattern + namespace name live here (Vite requires the
+// glob to be a string literal); all wiring is in ../esm-factory.mjs.
+import {i18nFromGlob} from '../esm-factory.mjs';
+
+const i18n = i18nFromGlob(import.meta.glob('../../locales/*/signup-form.json', {eager: true, import: 'default'}), 'signup-form');
+
+export default i18n;
+export const {LOCALE_DATA, SUPPORTED_LOCALES, generateResources} = i18n;
diff --git a/ghost/i18n/lib/require-loader.js b/ghost/i18n/lib/require-loader.js
new file mode 100644
index 00000000000..d30a29745af
--- /dev/null
+++ b/ghost/i18n/lib/require-loader.js
@@ -0,0 +1,13 @@
+// CJS-only resource loader: dynamic require against the on-disk locales tree.
+// Lives in its own module so the shared `i18n-core` stays free of dynamic
+// requires — the ESM/browser build never imports this file, so bundlers
+// (Vite/Rolldown/esbuild) never encounter the dynamic-require pattern.
+function requireLoader(locale, ns) {
+    try {
+        return require(`../locales/${locale}/${ns}.json`);
+    } catch (err) {
+        return require(`../locales/en/${ns}.json`);
+    }
+}
+
+module.exports = {requireLoader};
diff --git a/ghost/i18n/package.json b/ghost/i18n/package.json
index 95d3c67a6cb..49e63bb340e 100644
--- a/ghost/i18n/package.json
+++ b/ghost/i18n/package.json
@@ -7,20 +7,22 @@
   "main": "index.js",
   "exports": {
     ".": {
-      "browser": "./index.browser.js",
+      "types": "./index.d.ts",
+      "require": "./index.js",
       "default": "./index.js"
     },
-    "./lib/locale-data.json": "./lib/locale-data.json"
-  },
-  "browser": {
-    "./index.js": "./index.browser.js",
-    "./lib/i18n.js": "./lib/i18n.browser.js"
+    "./registry/*": {
+      "types": "./registry.d.ts",
+      "default": "./lib/registry/*.mjs"
+    },
+    "./lib/locale-data.json": "./lib/locale-data.json",
+    "./package.json": "./package.json"
   },
-  "types": "./build/i18n.d.ts",
+  "types": "./index.d.ts",
   "scripts": {
     "test:base": "NODE_ENV=testing vitest run --coverage",
     "test": "pnpm test:base && pnpm translate",
-    "lint:code": "eslint *.js lib/ --cache",
+    "lint:code": "eslint *.js *.mjs lib/ --cache",
     "lint": "pnpm lint:code && pnpm lint:test && pnpm lint:translations",
     "lint:test": "eslint test/ --cache",
     "lint:translations": "node ./test/i18n.lint.js",
@@ -33,7 +35,8 @@
   },
   "files": [
     "index.js",
-    "index.browser.js",
+    "index.d.ts",
+    "registry.d.ts",
     "lib",
     "locales"
   ],
diff --git a/ghost/i18n/registry.d.ts b/ghost/i18n/registry.d.ts
new file mode 100644
index 00000000000..d91c80bae49
--- /dev/null
+++ b/ghost/i18n/registry.d.ts
@@ -0,0 +1,13 @@
+// Types for the per-namespace subpath exports, e.g. '@tryghost/i18n/registry/portal'.
+import type {I18nFactory, LocaleDataEntry} from './index';
+
+declare const i18n: I18nFactory;
+
+export default i18n;
+export declare const LOCALE_DATA: LocaleDataEntry[];
+export declare const SUPPORTED_LOCALES: string[];
+export declare function generateResources(
+    locales: string[],
+    ns: string
+): Record<string, Record<string, Record<string, string>>>;
+export type {LocaleDataEntry};
diff --git a/ghost/i18n/test/i18n.test.js b/ghost/i18n/test/i18n.test.js
index 02638298954..9db4508f15b 100644
--- a/ghost/i18n/test/i18n.test.js
+++ b/ghost/i18n/test/i18n.test.js
@@ -5,82 +5,99 @@ const fsExtra = require('fs-extra');
 const i18n = require('../');
 
 describe('i18n', function () {
-    describe('browser entry', function () {
-        const browserI18n = require('../index.browser');
+    describe('ESM/browser entries (per-namespace static registries)', function () {
+        // The real browser path: each public app imports '@tryghost/i18n/registry/<ns>',
+        // resolved here from the actual shipped registry entries (lib/registry/*.mjs).
+        // There is no root ESM entry and no CJS "browser" entry any more — apps must use
+        // the per-namespace subpaths. These import()s cover ESM locale resolution, the
+        // English fallback and the theme-stub behaviour public apps rely on.
+        let portalI18n;
+        let ghostI18n;
+
+        beforeAll(async function () {
+            portalI18n = (await import('../lib/registry/portal.mjs')).default;
+            ghostI18n = (await import('../lib/registry/ghost.mjs')).default;
+        });
 
         it('loads bundled public app translations without server-only helpers', function () {
-            const t = browserI18n('nl', 'portal').t;
+            const t = portalI18n('nl', 'portal').t;
 
             assert.equal(t('Name'), 'Naam');
         });
 
-        it('uses the default namespace and locale', function () {
-            const t = browserI18n().t;
+        it('uses the default locale', function () {
+            const t = portalI18n().t;
 
             assert.equal(t('Name'), 'Name');
         });
 
         it('uses single curly braces for browser interpolation', function () {
-            const portalT = browserI18n('en', 'portal').t;
-            const ghostT = browserI18n('en', 'ghost').t;
+            const portalT = portalI18n('en', 'portal').t;
+            const ghostT = ghostI18n('en', 'ghost').t;
 
             assert.equal(portalT('Welcome, {name}', {name: '<b>John O\'Nolan</b>'}), 'Welcome, <b>John O\'Nolan</b>');
             assert.equal(ghostT('Welcome, {name}', {name: 'John'}), 'Welcome, John');
         });
 
-        it('uses default export translations when available', function () {
-            const translationFile = require(path.join(`../locales/`, 'nl', 'portal.json'));
-            const originalName = translationFile.Name;
-            const originalDefault = translationFile.default;
+        it('falls back to English for missing bundled locales', function () {
+            const resources = portalI18n.generateResources(['xx'], 'portal');
+            const englishResources = portalI18n.generateResources(['en'], 'portal');
 
-            translationFile.Name = undefined;
-            translationFile.default = {
-                Name: 'Naam'
-            };
+            assert.deepEqual(resources.xx, englishResources.en);
+        });
 
-            try {
-                const t = browserI18n('nl', 'portal').t;
-                assert.equal(t('Name'), 'Naam');
-            } finally {
-                translationFile.Name = originalName;
-                if (originalDefault === undefined) {
-                    delete translationFile.default;
-                } else {
-                    translationFile.default = originalDefault;
-                }
-            }
+        it('uses empty theme resources in browser builds', function () {
+            const instance = portalI18n('en', 'theme');
+
+            assert.deepEqual(instance.store.data.en.theme, {});
+            assert.equal(instance.t('Read more'), 'Read more');
         });
+    });
 
-        it('ignores non-object default exports', function () {
-            const translationFile = require(path.join(`../locales/`, 'nl', 'portal.json'));
-            const originalDefault = translationFile.default;
+    describe('CJS/ESM core parity', function () {
+        // lib/i18n-core.js (Node) and lib/i18n-core.mjs (browser) are deliberate
+        // twins: the browser path must be pure ESM (a CJS file leaks require()/
+        // module.exports into the UMD bundle and throws at load), while Ghost core
+        // require()s the package synchronously. This test guards against drift.
+        let cjsCore;
+        let esmCore;
 
-            translationFile.default = 'not an object';
+        beforeAll(async function () {
+            cjsCore = require('../lib/i18n-core');
+            esmCore = await import('../lib/i18n-core.mjs');
+        });
 
-            try {
-                const t = browserI18n('nl', 'portal').t;
-                assert.equal(t('Name'), 'Naam');
-            } finally {
-                if (originalDefault === undefined) {
-                    delete translationFile.default;
-                } else {
-                    translationFile.default = originalDefault;
-                }
-            }
+        it('exposes identical locale data and supported locales', function () {
+            assert.deepEqual(esmCore.SUPPORTED_LOCALES, cjsCore.SUPPORTED_LOCALES);
+            assert.deepEqual(esmCore.LOCALE_DATA, cjsCore.LOCALE_DATA);
         });
 
-        it('falls back to English for missing bundled locales', function () {
-            const resources = browserI18n.generateResources(['xx'], 'portal');
-            const englishResources = browserI18n.generateResources(['en'], 'portal');
+        it('mergeDefaultExport behaves identically', function () {
+            const input = {Name: 'Direct', default: {Name: 'FromDefault', Extra: 'x'}};
 
-            assert.deepEqual(resources.xx, englishResources.en);
+            assert.deepEqual(esmCore.mergeDefaultExport(input), cjsCore.mergeDefaultExport(input));
         });
 
-        it('uses empty theme resources in browser builds', function () {
-            const instance = browserI18n('en', 'theme');
+        it('createGenerateResources produces identical output for the same loader', function () {
+            const loader = locale => (locale === 'en' ? {Name: 'English'} : {Name: locale});
+            const esmGen = esmCore.createGenerateResources(loader);
+            const cjsGen = cjsCore.createGenerateResources(loader);
 
-            assert.deepEqual(instance.store.data.en.theme, {});
-            assert.equal(instance.t('Read more'), 'Read more');
+            assert.deepEqual(esmGen(['de', 'xx'], 'portal'), cjsGen(['de', 'xx'], 'portal'));
+        });
+
+        it('createI18n produces instances that translate identically', function () {
+            const generateResources = locales => locales.reduce((acc, l) => {
+                acc[l] = {portal: {Hello: l === 'nl' ? 'Hallo' : 'Hello'}};
+                return acc;
+            }, {});
+            const generateThemeResources = lng => ({[lng]: {theme: {}}});
+
+            const esm = esmCore.createI18n({generateResources, generateThemeResources})('nl', 'portal');
+            const cjs = cjsCore.createI18n({generateResources, generateThemeResources})('nl', 'portal');
+
+            assert.equal(esm.t('Hello'), 'Hallo');
+            assert.equal(esm.t('Hello'), cjs.t('Hello'));
         });
     });
 
@@ -105,6 +122,58 @@ describe('i18n', function () {
         assert.equal(t('Name'), 'Naam');
     });
 
+    it('generateResources (CJS require path) resolves locales and falls back to English', function () {
+        const resources = i18n.generateResources(['nl', 'xx'], 'portal');
+
+        assert.equal(resources.nl.portal.Name, 'Naam');
+        // 'xx' is not a bundled locale — the require loader falls back to English.
+        assert.equal(resources.xx.portal.Name, i18n.generateResources(['en'], 'portal').en.portal.Name);
+    });
+
+    describe('createGenerateResources', function () {
+        // Unit-tests the injectable-loader factory directly (the shape the static ESM
+        // registry uses), covering the English fallback + floor without a bundler.
+        const {createGenerateResources} = require('../lib/i18n-core');
+
+        it('uses the loaded resource when present', function () {
+            const gen = createGenerateResources((locale, ns) => ({[`${locale}.${ns}`]: 'hit'}));
+            const res = gen(['de'], 'ghost');
+
+            assert.equal(res.de.ghost['de.ghost'], 'hit');
+        });
+
+        it('falls back to English when a locale is missing (undefined)', function () {
+            const gen = createGenerateResources(locale => (locale === 'en' ? {Name: 'English'} : undefined));
+            const res = gen(['xx'], 'portal');
+
+            assert.equal(res.xx.portal.Name, 'English');
+        });
+
+        it('floors to an empty object when even English is missing', function () {
+            // Loader always returns undefined — the English floor must prevent
+            // mergeDefaultExport(undefined) from throwing.
+            const gen = createGenerateResources(() => undefined);
+
+            assert.doesNotThrow(() => gen(['xx'], 'portal'));
+            const res = gen(['xx'], 'portal');
+            assert.deepEqual(res.xx.portal, {});
+        });
+
+        it('merges an object default export onto the resource', function () {
+            const gen = createGenerateResources(() => ({Name: 'Direct', default: {Name: 'FromDefault'}}));
+            const res = gen(['de'], 'portal');
+
+            assert.equal(res.de.portal.Name, 'FromDefault');
+        });
+
+        it('ignores a non-object default export', function () {
+            const gen = createGenerateResources(() => ({Name: 'Direct', default: 'not-an-object'}));
+            const res = gen(['de'], 'portal');
+
+            assert.equal(res.de.portal.Name, 'Direct');
+        });
+    });
+
     describe('Can use Portal resources', function () {
         describe('Dutch', function () {
             let t;
diff --git a/ghost/i18n/vitest.config.mjs b/ghost/i18n/vitest.config.mjs
index 6be6b51c2ff..10a2ed63a7d 100644
--- a/ghost/i18n/vitest.config.mjs
+++ b/ghost/i18n/vitest.config.mjs
@@ -4,12 +4,27 @@ export default defineConfig({
     test: {
         globals: true,
         include: ['test/**/*.test.js'],
+        // The registry entries use Vite's import.meta.glob, so they MUST be
+        // Vitest-transformed (not externalized) or the glob stays an unresolved runtime
+        // call. The CJS lib/i18n-core.js is covered by the CJS suite; the ESM path uses
+        // the separate lib/i18n-core.mjs twin, so there's no shared-instance coverage
+        // issue to work around.
         coverage: {
             provider: 'v8',
             include: [
                 'index.js',
                 'lib/**/*.js'
             ],
+            // The ESM entries (lib/esm-factory.mjs, lib/registry/*.mjs) re-import the CJS
+            // lib/i18n-core.js under ESM, which v8 would instrument as a phantom second
+            // copy and mis-count its branches. The CJS test suite fully covers
+            // i18n-core.js; the ESM entries' behaviour is asserted in the
+            // 'ESM/browser entries' block. Keep them out of the coverage transform so the
+            // 100% thresholds stay meaningful and honest.
+            exclude: [
+                'lib/esm-factory.mjs',
+                'lib/registry/**'
+            ],
             reporter: ['text', 'cobertura'],
             thresholds: {
                 lines: 100,