feat: i18n support with first translations

tests/engine/i18nLocaleCompleteness.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from 'vitest';
+import en from '../../src/main/shared/i18n/locales/en.json';
+import de from '../../src/main/shared/i18n/locales/de.json';
+import fr from '../../src/main/shared/i18n/locales/fr.json';
+import itLocale from '../../src/main/shared/i18n/locales/it.json';
+import es from '../../src/main/shared/i18n/locales/es.json';
+
+type LocaleMap = Record<string, string>;
+
+const locales: Record<string, LocaleMap> = {
+  de: de as LocaleMap,
+  fr: fr as LocaleMap,
+  it: itLocale as LocaleMap,
+  es: es as LocaleMap,
+};
+
+describe('main/shared locale completeness', () => {
+  const englishKeys = Object.keys(en as LocaleMap).sort();
+
+  it('all main/shared locales contain exactly the english key set', () => {
+    for (const [locale, messages] of Object.entries(locales)) {
+      const localeKeys = Object.keys(messages).sort();
+
+      expect(localeKeys, `Locale ${locale} is missing or has extra keys`).toEqual(englishKeys);
+    }
+  });
+});