fix: use user locale instead of hardcoded de-DE for number/date formatting — closes #144

- CurrencyWidget: format numbers with user's locale
- ReservationModal: date formatting uses locale
- TripPDF: locale fallback to browser default instead of de-DE
- holidays.ts: formatDate accepts optional locale parameter

client/src/components/Dashboard/CurrencyWidget.tsx

@@ -14,7 +14,7 @@ const CURRENCIES = [
 const CURRENCY_OPTIONS = CURRENCIES.map(c => ({ value: c, label: c }))
 
 export default function CurrencyWidget() {
-  const { t } = useTranslation()
+  const { t, locale } = useTranslation()
   const [from, setFrom] = useState(() => localStorage.getItem('currency_from') || 'EUR')
   const [to, setTo] = useState(() => localStorage.getItem('currency_to') || 'USD')
   const [amount, setAmount] = useState('100')
@@ -40,7 +40,7 @@ export default function CurrencyWidget() {
   const rawResult = rate && amount ? (parseFloat(amount) * rate).toFixed(2) : null
   const formatNumber = (num) => {
     if (!num || num === '—') return '—'
-    return parseFloat(num).toLocaleString('de-DE', { minimumFractionDigits: 2, maximumFractionDigits: 2 })
+    return parseFloat(num).toLocaleString(locale, { minimumFractionDigits: 2, maximumFractionDigits: 2 })
   }
   const result = rawResult
 

client/src/components/PDF/TripPDF.tsx

@@ -110,7 +110,7 @@ interface downloadTripPDFProps {
 
 export async function downloadTripPDF({ trip, days, places, assignments, categories, dayNotes, reservations = [], t: _t, locale: _locale }: downloadTripPDFProps) {
   await ensureRenderer()
-  const loc = _locale || 'de-DE'
+  const loc = _locale || undefined
   const tr = _t || (k => k)
   const sorted = [...(days || [])].sort((a, b) => a.day_number - b.day_number)
   const range = longDateRange(sorted, loc)

client/src/components/Planner/ReservationModal.tsx

@@ -573,5 +573,5 @@ export function ReservationModal({ isOpen, onClose, onSave, reservation, days, p
 function formatDate(dateStr, locale) {
   if (!dateStr) return ''
   const d = new Date(dateStr + 'T00:00:00')
-  return d.toLocaleDateString(locale || 'de-DE', { day: 'numeric', month: 'short' })
+  return d.toLocaleDateString(locale || undefined, { day: 'numeric', month: 'short' })
 }

client/src/components/Vacay/holidays.ts

@@ -122,9 +122,9 @@ export function daysInMonth(year: number, month: number): number {
   return new Date(year, month, 0).getDate()
 }
 
-export function formatDate(dateStr: string): string {
+export function formatDate(dateStr: string, locale?: string): string {
   const d = new Date(dateStr + 'T00:00:00')
-  return d.toLocaleDateString('de-DE', { weekday: 'short', day: '2-digit', month: '2-digit', year: 'numeric' })
+  return d.toLocaleDateString(locale || undefined, { weekday: 'short', day: '2-digit', month: '2-digit', year: 'numeric' })
 }
 
 export { BUNDESLAENDER }