Set default locale according to browser locale (#11805)

We didn't get much complaints on Localization so I guess we can expand
it more and make it the default behavior to use the browser's locale
when you signup

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>

packages/twenty-shared/src/utils/validation/normalizeLocale.ts

@@ -0,0 +1,53 @@
+import { APP_LOCALES, SOURCE_LOCALE } from '@/translations';
+
+/**
+ * Maps language codes to full locale keys in APP_LOCALES
+ * Example: 'fr' -> 'fr-FR', 'en' -> 'en'
+ */
+const languageToLocaleMap = Object.keys(APP_LOCALES).reduce<
+  Record<string, string>
+>((map, locale) => {
+  // Extract the language code (part before the hyphen or the whole code if no hyphen)
+  const language = locale.split('-')[0].toLowerCase();
+
+  // Only add to the map if not already added or if the current locale is the source locale
+  // This ensures language codes map to their full locale version (e.g., 'es' -> 'es-ES')
+  // but preserves 'en' -> 'en' since it's the source locale
+  if (!map[language] || locale === SOURCE_LOCALE) {
+    map[language] = locale;
+  }
+
+  return map;
+}, {});
+
+/**
+ * Normalizes a locale string to match our supported formats
+ */
+export const normalizeLocale = (
+  value: string | null,
+): keyof typeof APP_LOCALES => {
+  if (value === null) {
+    return SOURCE_LOCALE;
+  }
+
+  // Direct match in our supported locales
+  if (value in APP_LOCALES) {
+    return value as keyof typeof APP_LOCALES;
+  }
+
+  // Try case-insensitive match (e.g., 'fr-fr' -> 'fr-FR')
+  const caseInsensitiveMatch = Object.keys(APP_LOCALES).find(
+    (locale) => locale.toLowerCase() === value.toLowerCase(),
+  );
+  if (caseInsensitiveMatch) {
+    return caseInsensitiveMatch as keyof typeof APP_LOCALES;
+  }
+
+  // Try matching just the language part (e.g., 'fr' -> 'fr-FR')
+  const languageCode = value?.trim() ? value.split('-')[0].toLowerCase() : '';
+  if (languageToLocaleMap[languageCode]) {
+    return languageToLocaleMap[languageCode] as keyof typeof APP_LOCALES;
+  }
+
+  return SOURCE_LOCALE;
+};