diff --git a/app/locale.ts b/app/locale.ts
index 7bcbc4c110..6bc050679b 100644
--- a/app/locale.ts
+++ b/app/locale.ts
@@ -10,9 +10,10 @@ import type { LoggerType } from '../ts/types/Logging';
 import type { LocaleMessagesType } from '../ts/types/I18N';
 import type { LocalizerType } from '../ts/types/Util';
 
-function normalizeLocaleName(locale: string): string {
-  if (/^en-/.test(locale)) {
-    return 'en';
+function removeRegion(locale: string): string {
+  const match = /^([^-]+)(-.+)$/.exec(locale);
+  if (match) {
+    return match[1];
   }
 
   return locale;
@@ -38,12 +39,29 @@ export type LocaleType = {
   messages: LocaleMessagesType;
 };
 
+function finalize(
+  messages: LocaleMessagesType,
+  backupMessages: LocaleMessagesType,
+  localeName: string
+) {
+  // We start with english, then overwrite that with anything present in locale
+  const finalMessages = merge(backupMessages, messages);
+
+  const i18n = setupI18n(localeName, finalMessages);
+
+  return {
+    i18n,
+    name: localeName,
+    messages: finalMessages,
+  };
+}
+
 export function load({
   appLocale,
   logger,
 }: {
   appLocale: string;
-  logger: Pick<LoggerType, 'error'>;
+  logger: Pick<LoggerType, 'error' | 'warn'>;
 }): LocaleType {
   if (!appLocale) {
     throw new TypeError('`appLocale` is required');
@@ -52,6 +70,9 @@ export function load({
   if (!logger || !logger.error) {
     throw new TypeError('`logger.error` is required');
   }
+  if (!logger.warn) {
+    throw new TypeError('`logger.warn` is required');
+  }
 
   const english = getLocaleMessages('en');
 
@@ -59,30 +80,23 @@ export function load({
   // default to 'en'
   //
   // possible locales:
-  // https://github.com/electron/electron/blob/master/docs/api/locales.md
-  let localeName = normalizeLocaleName(appLocale);
-  let messages;
+  // https://source.chromium.org/chromium/chromium/src/+/main:ui/base/l10n/l10n_util.cc
+  const normalized = removeRegion(appLocale);
 
   try {
-    messages = getLocaleMessages(localeName);
-
-    // We start with english, then overwrite that with anything present in locale
-    messages = merge(english, messages);
+    return finalize(getLocaleMessages(appLocale), english, appLocale);
   } catch (e) {
-    logger.error(
-      `Problem loading messages for locale ${localeName} ${e.stack}`
-    );
-    logger.error('Falling back to en locale');
-
-    localeName = 'en';
-    messages = english;
+    logger.warn(`Problem loading messages for locale ${appLocale}`);
   }
 
-  const i18n = setupI18n(appLocale, messages);
+  try {
+    logger.warn(`Falling back to parent language: '${normalized}'`);
+    // Note: messages are from parent language, but we still keep the region
+    return finalize(getLocaleMessages(normalized), english, appLocale);
+  } catch (e) {
+    logger.error(`Problem loading messages for locale ${normalized}`);
 
-  return {
-    i18n,
-    name: localeName,
-    messages,
-  };
+    logger.warn("Falling back to 'en' locale");
+    return finalize(english, english, 'en');
+  }
 }
diff --git a/app/main.ts b/app/main.ts
index 58aa3db5ee..ab6d54d25f 100644
--- a/app/main.ts
+++ b/app/main.ts
@@ -1585,7 +1585,7 @@ app.on('ready', async () => {
 
   if (!locale) {
     const appLocale = getAppLocale();
-    locale = loadLocale({ appLocale, logger });
+    locale = loadLocale({ appLocale, logger: getLogger() });
   }
 
   sqlInitPromise = initializeSQL(userDataPath);
diff --git a/ts/os-locale.d.ts b/ts/os-locale.d.ts
deleted file mode 100644
index a29cff0a8c..0000000000
--- a/ts/os-locale.d.ts
+++ /dev/null
@@ -1,10 +0,0 @@
-// Copyright 2021 Signal Messenger, LLC
-// SPDX-License-Identifier: AGPL-3.0-only
-
-// We need this until we upgrade os-locale. Newer versions include type definitions.
-
-// We can't upgrade it yet because we patch it to disable its findup/exec behavior.
-
-declare module 'os-locale' {
-  export function sync(): string;
-}
diff --git a/ts/test-node/app/menu_test.ts b/ts/test-node/app/menu_test.ts
index 8ff6276bea..7cff15d077 100644
--- a/ts/test-node/app/menu_test.ts
+++ b/ts/test-node/app/menu_test.ts
@@ -202,6 +202,9 @@ describe('createTemplate', () => {
       error(arg: unknown) {
         throw new Error(String(arg));
       },
+      warn(arg: unknown) {
+        throw new Error(String(arg));
+      },
     },
   });
 
diff --git a/ts/util/mapToSupportLocale.ts b/ts/util/mapToSupportLocale.ts
index aac60795cb..ed725f821c 100644
--- a/ts/util/mapToSupportLocale.ts
+++ b/ts/util/mapToSupportLocale.ts
@@ -15,6 +15,7 @@ export type SupportLocaleType =
   | 'sq'
   | 'zh-tw';
 
+// See https://source.chromium.org/chromium/chromium/src/+/main:ui/base/l10n/l10n_util.cc
 export type ElectronLocaleType =
   | 'af'
   | 'ar'
@@ -25,8 +26,19 @@ export type ElectronLocaleType =
   | 'cy'
   | 'da'
   | 'de'
+  | 'de-AT'
+  | 'de-CH'
+  | 'de-DE'
+  | 'de-LI'
   | 'el'
   | 'en'
+  | 'en-AU'
+  | 'en-CA'
+  | 'en-GB'
+  | 'en-GB-oxendict'
+  | 'en-IN'
+  | 'en-NZ'
+  | 'en-US'
   | 'eo'
   | 'es'
   | 'es_419'
@@ -35,12 +47,17 @@ export type ElectronLocaleType =
   | 'fa'
   | 'fi'
   | 'fr'
+  | 'fr-CA'
+  | 'fr-CH'
+  | 'fr-FR'
   | 'he'
   | 'hi'
   | 'hr'
   | 'hu'
   | 'id'
   | 'it'
+  | 'it-CH'
+  | 'it-IT'
   | 'ja'
   | 'km'
   | 'kn'
@@ -72,6 +89,7 @@ export type ElectronLocaleType =
   | 'ur'
   | 'vi'
   | 'zh_CN'
+  | 'zh-HK'
   | 'zh_TW';
 
 export function mapToSupportLocale(ourLocale: string): SupportLocaleType {