feat: add German and English UI language support

A single-language interface makes the app less usable for part of the audience
and encourages more hardcoded copy as new screens and states are added.
Introducing a shared i18n path with a persisted language preference gives the
UI one consistent way to present text and lowers the risk of partial or
inconsistent localization over time.

The surrounding copy cleanup belongs in the same change because it aligns
existing labels, messages, and settings text with that translation structure
instead of leaving mixed localization approaches in place.

README.md

@@ -25,7 +25,7 @@ Twitch client for the Steam Deck with Big-Screen UI, full gamepad control, and V
 
 ## Features
 
-- **Live Streams** — Ad-free playback via Streamlink + hls.js (HTML5 video, no external player)
+- **Live Streams** — Playback via Streamlink + hls.js (HTML5 video, no external player)
 - **VOD Playback** — Watch recordings with automatic resume at last position
 - **VOD Chapters** — Browse and jump to chapters within VODs; view count displayed on VOD cards
 - **Video Quality Selection** — Change stream quality on-the-fly during playback (Live and VOD); available qualities fetched dynamically via Streamlink; session-only, defaults to `best`
@@ -35,6 +35,7 @@ Twitch client for the Steam Deck with Big-Screen UI, full gamepad control, and V
 - **Twitch Login** — Device Code Flow with QR code (no browser required)
 - **Following** — Live status and overview of followed streamers
 - **Category Browser** — Browse Twitch categories and top streams
+- **UI Language Support** — Switch the interface between German and English in Settings; the selection is stored locally
 - **Language-Filtered Streams** — Top streams filtered by German/English
 - **Account Screen** — User profile, app version, logout
 - **VOD History** — Local SQLite database with playback history and progress
@@ -58,6 +59,7 @@ Shared (src/shared/)
 Electron (Renderer)
   ├── React UI      -- Screens: Login, Following, Browse, Category, Channel,
   │                    StreamList (DE/EN), Settings, Account
+  ├── i18n          -- German/English message catalogs + translation hook
   ├── VideoPlayer   -- hls.js <video> wrapper (forwardRef, imperative handle)
   ├── ChapterPanel  -- Chapter selection panel (during playback or VOD start)
   ├── QualityPanel  -- Quality selection panel
@@ -213,6 +215,7 @@ The script handles automatically:
 - **Twitch-Login** — Device Code Flow mit QR-Code (kein Browser noetig)
 - **Gefolgte Kanaele** — Live-Status und Uebersicht der gefolgten Streamer
 - **Kategorie-Browser** — Twitch-Kategorien und Top-Streams durchsuchen
+- **UI-Sprachsupport** — Oberflaeche in den Einstellungen zwischen Deutsch und Englisch umschalten; Auswahl wird lokal gespeichert
 - **Sprachgefilterte Streams** — Top-Streams gefiltert nach Deutsch/Englisch
 - **Account-Ansicht** — Nutzerprofil, App-Version, Abmelden
 - **VOD-Verlauf** — Lokale SQLite-Datenbank mit Wiedergabe-Historie und Fortschritt
@@ -236,6 +239,7 @@ Geteilt (src/shared/)
 Electron (Renderer)
   ├── React UI      -- Screens: Login, Following, Browse, Category, Channel,
   │                    StreamList (DE/EN), Settings, Account
+  ├── i18n          -- Deutsche/englische Message-Kataloge + Uebersetzungs-Hook
   ├── VideoPlayer   -- hls.js <video> Wrapper (forwardRef, imperative handle)
   ├── ChapterPanel  -- Kapitel-Auswahl-Panel (waehrend Wiedergabe oder VOD-Start)
   ├── QualityPanel  -- Qualitaets-Auswahl-Panel