Use LocaleMatcher to resolve system preferred locales

ts/test-node/app/locale_test.ts

@@ -0,0 +1,46 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+import { load } from '../../../app/locale';
+import type { LoggerType } from '../../types/Logging';
+
+const logger: Pick<LoggerType, 'info' | 'warn'> = {
+  info(..._args: Array<unknown>) {
+    // noop
+  },
+  warn(..._args: Array<unknown>) {
+    throw new Error(String(_args));
+  },
+};
+
+describe('locale', async () => {
+  describe('load', () => {
+    it('resolves expected locales correctly', async () => {
+      async function testCase(
+        preferredSystemLocales: Array<string>,
+        expectedLocale: string
+      ) {
+        const actualLocale = await load({ preferredSystemLocales, logger });
+        assert.strictEqual(actualLocale.name, expectedLocale);
+      }
+
+      // Basic tests
+      await testCase(['en'], 'en');
+      await testCase(['es'], 'es');
+      await testCase(['fr', 'hk'], 'fr');
+      await testCase(['fr-FR', 'hk'], 'fr');
+      await testCase(['fa-UK'], 'fa-IR');
+      await testCase(['an', 'fr-FR'], 'fr'); // If we ever add support for Aragonese, this test will fail.
+
+      // Specific cases we want to ensure work as expected
+      await testCase(['zh-Hant-TW'], 'zh-TW');
+      await testCase(['zh-Hant-HK'], 'zh-HK');
+      await testCase(['zh'], 'zh-CN');
+      await testCase(['yue'], 'yue');
+      await testCase(['ug'], 'ug');
+      await testCase(['nn', 'nb'], 'nb');
+      await testCase(['es-419'], 'es');
+    });
+  });
+});

ts/test-node/app/menu_test.ts

@@ -202,9 +202,6 @@ describe('createTemplate', () => {
       info(_arg: unknown) {
         // noop
       },
-      error(arg: unknown) {
-        throw new Error(String(arg));
-      },
       warn(arg: unknown) {
         throw new Error(String(arg));
       },