- Full translations for all UI strings in 7 languages
- Language picker shows native names (Français, Italiano, Español, Português, Русский)
- Auto-detection via navigator.languages
- Cyrillic font subset for Russian (Inter, 19KB)
- Footer shared across all languages (untranslated links)
- Self-host Inter and JetBrains Mono (woff2, 69KB total)
- Remove Google Fonts dependency entirely (no external requests)
- Service Worker pre-caches font files
- Eliminate font-swap layout shifts
- WCAG contrast fix: disabled button uses solid color instead of opacity
- Footer link always underlined for distinguishability
- Translated aria-labels via data-i18n-aria
- Dimmed QR with "Bezahlt" stamp on paid invoices
- Hide wallet/address buttons when invoice is paid
