Multilanguage: Deutsch / English, umschaltbar in Einstellungen

- i18n.js: Übersetzungsmodul mit t(), setLang(), applyLang() + vollst. DE/EN Wörterbuch
- Backend: language-Feld in UserSettings, Migration, Settings-API
- calendar.js: alle deutschen Strings auf t()-Aufrufe umgestellt, setLang() beim Start
- app.js, api.js, color-picker.js, views/*.js: alle UI-Strings übersetzt
- Sprach-Dropdown in Einstellungen > Darstellung, data-i18n-Attribute in index.html

frontend/js/views/agenda.js

@@ -1,11 +1,9 @@
 import { isPast } from '../utils.js';
-
-const DOW = ['Sonntag','Montag','Dienstag','Mittwoch','Donnerstag','Freitag','Samstag'];
-const MON  = ['Jan','Feb','Mär','Apr','Mai','Jun','Jul','Aug','Sep','Okt','Nov','Dez'];
+import { t, getLang } from '../i18n.js';
 
 export function renderAgenda(container, currentDate, events, onEventClick) {
   if (!events.length) {
-    container.innerHTML = `<div class="agenda-view"><div class="agenda-empty">Keine Termine im angezeigten Zeitraum</div></div>`;
+    container.innerHTML = `<div class="agenda-view"><div class="agenda-empty">${t('no_events')}</div></div>`;
     return;
   }
 
@@ -35,7 +33,7 @@ export function renderAgenda(container, currentDate, events, onEventClick) {
       .map(ev => {
         const color = ev.color || ev.calendarColor || '#4285f4';
         const pastCls = isPast(ev) ? 'past' : '';
-        let timeStr = 'Ganztägig';
+        let timeStr = t('allday_cap');
         if (!ev.allDay) {
           const s = new Date(ev.start);
           const e = new Date(ev.end);
@@ -57,8 +55,8 @@ export function renderAgenda(container, currentDate, events, onEventClick) {
       <div class="agenda-date ${todayCls}">
         <div class="agenda-date-num">${date.getDate()}</div>
         <div class="agenda-date-label">
-          <span class="wd">${DOW[date.getDay()]}</span>
-          <span class="mo">${MON[date.getMonth()]} ${date.getFullYear()}</span>
+          <span class="wd">${t('days_long')[date.getDay()]}</span>
+          <span class="mo">${t('months_short')[date.getMonth()]} ${date.getFullYear()}</span>
         </div>
       </div>
       ${evHtml}
@@ -83,7 +81,7 @@ function isTodayDate(d) {
 }
 
 function fmtTime(d) {
-  return d.toLocaleTimeString('de', { hour: '2-digit', minute: '2-digit' });
+  return d.toLocaleTimeString(getLang(), { hour: '2-digit', minute: '2-digit' });
 }
 
 function escHtml(s) {

frontend/js/views/month.js

@@ -1,12 +1,10 @@
 import { formatDate, isSameDay, isToday, isPast, dayOfWeek, getISOWeekNumber } from '../utils.js';
-
-const DOW_MONDAY = ['Mo', 'Di', 'Mi', 'Do', 'Fr', 'Sa', 'So'];
-const DOW_SUNDAY = ['So', 'Mo', 'Di', 'Mi', 'Do', 'Fr', 'Sa'];
+import { t } from '../i18n.js';
 
 export function renderMonth(container, currentDate, events, onDayClick, onEventClick, weekStartDay = 'monday') {
   const year = currentDate.getFullYear();
   const month = currentDate.getMonth();
-  const DOW = weekStartDay === 'sunday' ? DOW_SUNDAY : DOW_MONDAY;
+  const DOW = weekStartDay === 'sunday' ? t('dow_sunday') : t('dow_monday');
 
   const firstDay = new Date(year, month, 1);
   const lastDay  = new Date(year, month + 1, 0);
@@ -82,7 +80,7 @@ export function renderMonth(container, currentDate, events, onDayClick, onEventC
       }).join('');
 
       const moreHtml = hiddenCount > 0
-        ? `<div class="month-more" data-date="${key}">+${hiddenCount} weitere</div>`
+        ? `<div class="month-more" data-date="${key}">${t('more_events', {n: hiddenCount})}</div>`
         : '';
 
       cellsHtml += `<div class="month-cell ${todayClass} ${otherClass}" data-date="${key}">

frontend/js/views/week.js

@@ -1,6 +1,5 @@
 import { isToday, isPast, dayOfWeek, weekStart, getISOWeekNumber } from '../utils.js';
-
-const DOW_SHORT = ['So', 'Mo', 'Di', 'Mi', 'Do', 'Fr', 'Sa'];
+import { t } from '../i18n.js';
 
 export function renderWeek(container, currentDate, events, onSlotClick, onEventClick, isSingleDay = false, weekStartDay = 'monday', hourH = 60) {
   // Build the days array (7 days for week, 1 for day)
@@ -23,14 +22,14 @@ export function renderWeek(container, currentDate, events, onSlotClick, onEventC
   // ── KW Badge ──────────────────────────────────────────
   const kwNum = getISOWeekNumber(days[0]);
   const kwBadge = !isSingleDay
-    ? `<div class="week-kw-badge">KW ${kwNum}</div>`
+    ? `<div class="week-kw-badge">${t('week_abbr')} ${kwNum}</div>`
     : '';
 
   // ── Header ────────────────────────────────────────────
   const headerCols = days.map(day => {
     const todayCls = isToday(day) ? 'today' : '';
     return `<div class="week-day-header ${todayCls}" data-date="${dayKey(day)}">
-      <div class="day-name">${DOW_SHORT[day.getDay()]}</div>
+      <div class="day-name">${t('dow_index')[day.getDay()]}</div>
       <div class="day-num">${day.getDate()}</div>
     </div>`;
   }).join('');
@@ -105,7 +104,7 @@ export function renderWeek(container, currentDate, events, onSlotClick, onEventC
       ${headerCols}
     </div>
     <div class="week-allday-row">
-      <div class="allday-gutter">ganztägig</div>
+      <div class="allday-gutter">${t('allday')}</div>
       <div class="allday-cols">${alldayCols}</div>
     </div>
     <div class="week-body">