feat: add i18n module (public/i18n.js)

public/i18n.js

@@ -0,0 +1,97 @@
+/**
+ * i18n — Internationalisierung / Übersetzungsmodul
+ * Bietet t(), initI18n(), setLocale(), getLocale(), getSupportedLocales(),
+ * formatDate(), formatTime() für die gesamte App.
+ * Dependencies: none (vanilla JS, Fetch API, Intl API)
+ */
+
+const SUPPORTED_LOCALES = ['de', 'en'];
+const DEFAULT_LOCALE = 'de';
+const STORAGE_KEY = 'oikos-locale';
+
+let currentLocale = DEFAULT_LOCALE;
+let translations = {};
+let fallbackTranslations = {};
+
+/** Resolve locale: manual override > navigator.language > default */
+function resolveLocale() {
+  const stored = localStorage.getItem(STORAGE_KEY);
+  if (stored && SUPPORTED_LOCALES.includes(stored)) return stored;
+
+  const browserLocales = navigator.languages || [navigator.language];
+  for (const tag of browserLocales) {
+    const base = tag.split('-')[0].toLowerCase();
+    if (SUPPORTED_LOCALES.includes(base)) return base;
+  }
+  return DEFAULT_LOCALE;
+}
+
+/** Lade eine Locale-JSON-Datei */
+async function loadLocale(locale) {
+  const resp = await fetch(`/locales/${locale}.json`);
+  if (!resp.ok) throw new Error(`Failed to load locale: ${locale}`);
+  return resp.json();
+}
+
+/** Initialisierung — einmal beim App-Start aufrufen */
+export async function initI18n() {
+  currentLocale = resolveLocale();
+  fallbackTranslations = await loadLocale(DEFAULT_LOCALE);
+  if (currentLocale !== DEFAULT_LOCALE) {
+    translations = await loadLocale(currentLocale);
+  } else {
+    translations = fallbackTranslations;
+  }
+  document.documentElement.lang = currentLocale;
+}
+
+/** Sprache wechseln — löst 'locale-changed' Event aus */
+export async function setLocale(locale) {
+  if (!SUPPORTED_LOCALES.includes(locale)) return;
+  localStorage.setItem(STORAGE_KEY, locale);
+  currentLocale = locale;
+  if (locale === DEFAULT_LOCALE) {
+    translations = fallbackTranslations;
+  } else {
+    translations = await loadLocale(locale);
+  }
+  document.documentElement.lang = locale;
+  window.dispatchEvent(new CustomEvent('locale-changed', { detail: { locale } }));
+}
+
+/** Übersetzungsfunktion mit Platzhalter-Unterstützung {{variable}} */
+export function t(key, params = {}) {
+  let str = translations[key] ?? fallbackTranslations[key] ?? key;
+  for (const [k, v] of Object.entries(params)) {
+    str = str.replaceAll(`{{${k}}}`, String(v));
+  }
+  return str;
+}
+
+/** Aktuelle Locale abfragen */
+export function getLocale() {
+  return currentLocale;
+}
+
+/** Liste der unterstützten Locales */
+export function getSupportedLocales() {
+  return [...SUPPORTED_LOCALES];
+}
+
+/** Datum locale-aware formatieren */
+export function formatDate(date) {
+  return new Intl.DateTimeFormat(currentLocale, {
+    day: '2-digit',
+    month: '2-digit',
+    year: 'numeric',
+  }).format(date instanceof Date ? date : new Date(date));
+}
+
+/** Uhrzeit locale-aware formatieren */
+export function formatTime(date) {
+  return new Intl.DateTimeFormat(currentLocale, {
+    hour: '2-digit',
+    minute: '2-digit',
+    hour12: false,
+  }).format(date instanceof Date ? date : new Date(date));
+}