diff --git a/README.md b/README.md
index 25155152..ffd73d5e 100644
--- a/README.md
+++ b/README.md
@@ -220,7 +220,7 @@ To add a new translation key you can do these steps:
 
 1. Add the new key entry to the code where the new key is used: `t("some_new_key")`
 1. Run `yarn i18n` to extract the new key and update the translation files. This
-   will add a skeleton entry to the `locales/en-GB/app.json` file:
+   will add a skeleton entry to the `locales/en/app.json` file:
    ```jsonc
    {
        ...
@@ -228,7 +228,7 @@ To add a new translation key you can do these steps:
        ...
    }
    ```
-1. Update the skeleton entry in the `locales/en-GB/app.json` file with
+1. Update the skeleton entry in the `locales/en/app.json` file with
    the English translation:
 
 ```jsonc
diff --git a/i18next-parser.config.ts b/i18next-parser.config.ts
index 7d71d727..3acf2b5e 100644
--- a/i18next-parser.config.ts
+++ b/i18next-parser.config.ts
@@ -21,7 +21,7 @@ export default {
       },
     ],
   },
-  locales: ["en-GB"],
+  locales: ["en"],
   output: "locales/$LOCALE/$NAMESPACE.json",
   input: ["src/**/*.{ts,tsx}"],
   sort: true,
diff --git a/localazy.json b/localazy.json
index 2b9f713c..823e4a3e 100644
--- a/localazy.json
+++ b/localazy.json
@@ -7,13 +7,13 @@
     "features": ["plural_postfix_us", "filter_untranslated"],
     "files": [
       {
-        "pattern": "locales/en-GB/*.json",
+        "pattern": "locales/en/*.json",
         "lang": "inherited"
       },
       {
         "group": "existing",
         "pattern": "locales/*/*.json",
-        "excludes": ["locales/en-GB/*.json"],
+        "excludes": ["locales/en/*.json"],
         "lang": "${autodetectLang}"
       }
     ]
@@ -25,9 +25,6 @@
         "output": "locales/${langLsrDash}/${file}"
       }
     ],
-    "includeSourceLang": "${includeSourceLang|false}",
-    "langAliases": {
-      "en": "en_GB"
-    }
+    "includeSourceLang": "${includeSourceLang|false}"
   }
 }
diff --git a/locales/en-GB/app.json b/locales/en/app.json
similarity index 100%
rename from locales/en-GB/app.json
rename to locales/en/app.json
diff --git a/src/@types/i18next.d.ts b/src/@types/i18next.d.ts
index 4a8830da..3c65e620 100644
--- a/src/@types/i18next.d.ts
+++ b/src/@types/i18next.d.ts
@@ -7,7 +7,7 @@ Please see LICENSE in the repository root for full details.
 
 import "i18next";
 // import all namespaces (for the default language, only)
-import app from "../../locales/en-GB/app.json";
+import app from "../../locales/en/app.json";
 
 declare module "i18next" {
   interface CustomTypeOptions {
diff --git a/src/TranslatedError.ts b/src/TranslatedError.ts
index 0dbe675a..420556be 100644
--- a/src/TranslatedError.ts
+++ b/src/TranslatedError.ts
@@ -22,7 +22,7 @@ export abstract class TranslatedError extends Error {
     messageKey: ParseKeys<DefaultNamespace, TOptions>,
     translationFn: TFunction<DefaultNamespace>,
   ) {
-    super(translationFn(messageKey, { lng: "en-GB" } as TOptions));
+    super(translationFn(messageKey, { lng: "en" } as TOptions));
     this.translatedMessage = translationFn(messageKey);
   }
 }
diff --git a/src/initializer.tsx b/src/initializer.tsx
index 47634078..e9290504 100644
--- a/src/initializer.tsx
+++ b/src/initializer.tsx
@@ -24,7 +24,7 @@ import { platform } from "./Platform";
 
 // This generates a map of locale names to their URL (based on import.meta.url), which looks like this:
 // {
-//   "../locales/en-GB/app.json": "/whatever/assets/root/locales/en-aabbcc.json",
+//   "../locales/en/app.json": "/whatever/assets/root/locales/en-aabbcc.json",
 //   ...
 // }
 const locales = import.meta.glob<string>("../locales/*/*.json", {
@@ -41,7 +41,7 @@ const getLocaleUrl = (
 const supportedLngs = [
   ...new Set(
     Object.keys(locales).map((url) => {
-      // The URLs are of the form ../locales/en-GB/app.json
+      // The URLs are of the form ../locales/en/app.json
       // This extracts the language code from the URL
       const lang = url.match(/\/([^/]+)\/[^/]+\.json$/)?.[1];
       if (!lang) {
@@ -133,7 +133,7 @@ export class Initializer {
       .use(languageDetector)
       .use(initReactI18next)
       .init({
-        fallbackLng: "en-GB",
+        fallbackLng: "en",
         defaultNS: "app",
         keySeparator: ".",
         nsSeparator: false,
diff --git a/src/vitest.setup.ts b/src/vitest.setup.ts
index 38b8704e..46b370a9 100644
--- a/src/vitest.setup.ts
+++ b/src/vitest.setup.ts
@@ -17,20 +17,20 @@ import "vitest-axe/extend-expect";
 import { logger } from "matrix-js-sdk/src/logger";
 import "@testing-library/jest-dom/vitest";
 
-import EN_GB from "../locales/en-GB/app.json";
+import EN from "../locales/en/app.json";
 import { Config } from "./config/Config";
 
 // Bare-minimum i18n config
 i18n
   .use(initReactI18next)
   .init({
-    lng: "en-GB",
-    fallbackLng: "en-GB",
-    supportedLngs: ["en-GB"],
+    lng: "en",
+    fallbackLng: "en",
+    supportedLngs: ["en"],
     // We embed the translations, so that it never needs to fetch
     resources: {
-      "en-GB": {
-        app: EN_GB,
+      en: {
+        app: EN,
       },
     },
     interpolation: {