Recognise en-US and other English variants as the source in check

CHANGELOG.md

@@ -5,6 +5,7 @@ All notable changes to this project will be documented in this file.
 ## [Unreleased]
 
 ### Fixed
+- `check` run without a `localhero.json` recognises a regional English file (`en-US.json`, `en_US.yml`, `en-GB`) as the source. Before, it only matched a plain `en` and otherwise picked the language with the most keys, which in many JavaScript projects named after `en-US` meant checking every locale against, say, Arabic. US English wins when several English variants exist.
 - `check` no longer flags a gettext plural form for using a placeholder only the plural source has ("Moved down 1 place." / "%(counter)s places"), or an ICU translation for saying the number with `#` instead of repeating `{n}`. Rails and i18next placeholders are still counted, so a dropped repeat like a second `%{days}` is still reported.
 - `check --source <locale>` with no files for that locale now fails with a message instead of reporting 0 keys and 100% complete.
 - `check` run without a `localhero.json` now finds locale folders below the project root, such as `packages/app/locales` or `apps/web/public/locales` in a monorepo, when the usual folder holds none. It checks the folder with the most languages and names any others it found, each checkable with `--path`. Folders under `node_modules`, `vendor`, build output, virtual environments and test fixtures are left out. Before, the run stopped with "No translation files found".

src/commands/check.ts

@@ -278,7 +278,7 @@ const SOURCE_REASONS: Record<DetectedSetup['reason'], string> = {
   option: 'from --source',
   gettext: 'its catalog is untranslated',
   template: 'from the .pot template',
-  en: 'en is present',
+  en: 'English is present',
   guessed: 'guessed from the most keys'
 };
 

src/utils/locale-detection.ts

@@ -70,6 +70,13 @@ export function looksLikeGettextSource(content: string): boolean {
   return untranslated.length / entries.length >= GETTEXT_SOURCE_SHARE;
 }
 
+// en-US.json is the most common English file name in JavaScript projects.
+function englishLocale(locales: string[]): string | null {
+  if (locales.includes('en')) return 'en';
+  const variants = locales.filter((locale) => /^en[-_]/i.test(locale));
+  return variants.find((locale) => /^en[-_]us$/i.test(locale)) ?? variants.sort()[0] ?? null;
+}
+
 export function chooseSourceLocale(input: {
   explicit?: string;
   locales: string[];
@@ -82,7 +89,8 @@ export function chooseSourceLocale(input: {
   if (gettextSources.length === 1) return { locale: gettextSources[0], reason: 'gettext' };
   if (hasTemplate) return { locale: 'en', reason: 'template' };
   if (locales.length === 0) return null;
-  if (locales.includes('en')) return { locale: 'en', reason: 'en' };
+  const english = englishLocale(locales);
+  if (english) return { locale: english, reason: 'en' };
 
   const [mostKeys] = [...locales].sort((a, b) => (keyCounts[b] ?? 0) - (keyCounts[a] ?? 0));
   return { locale: mostKeys, reason: 'guessed' };

tests/utils/locale-detection.test.ts

@@ -105,6 +105,19 @@ describe('chooseSourceLocale', () => {
     expect(chooseSourceLocale({ locales, keyCounts, gettextSources: [], hasTemplate: false })).toEqual({ locale: 'en', reason: 'en' });
   });
 
+  it('picks a regional English locale over the one with the most keys', () => {
+    const counts = { 'de-DE': 120, 'en-US': 100, 'ar-EG': 130 };
+    expect(chooseSourceLocale({ locales: ['de-DE', 'en-US', 'ar-EG'], keyCounts: counts, gettextSources: [], hasTemplate: false })).toEqual({ locale: 'en-US', reason: 'en' });
+  });
+
+  it.each([
+    [['en-GB', 'en-US', 'sv'], 'en-US'],
+    [['en_GB', 'en_US', 'sv'], 'en_US'],
+    [['en-GB', 'sv'], 'en-GB']
+  ])('prefers US English among English variants in %j', (variants, expected) => {
+    expect(chooseSourceLocale({ locales: variants, keyCounts: {}, gettextSources: [], hasTemplate: false })).toEqual({ locale: expected, reason: 'en' });
+  });
+
   it('guesses the locale with the most keys otherwise', () => {
     expect(chooseSourceLocale({ locales: ['sv', 'de'], keyCounts, gettextSources: [], hasTemplate: false })).toEqual({ locale: 'sv', reason: 'guessed' });
   });