Where the on-device Translator/LanguageDetector APIs are missing,
Settings said to use Chrome/Edge "or the Lotus desktop app", but the
Linux and macOS apps (WebKit) lack them too, and showed the advice to
people already in the app. Word it by platform. (The per-message
Translate action was already hidden where unsupported.)
Fixes#349
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5
Add per-message translation that runs entirely on-device via the
Chromium built-in Translator + LanguageDetector APIs. Message text
never leaves the machine and never touches a cloud service, preserving
the E2EE guarantee. When the on-device engine is unavailable
(non-Chromium / mobile) the feature simply hides itself; there is no
network fallback.
- Engine abstraction (utils/translation): TranslationEngine interface
plus a chromeTranslationEngine implementation (feature-detected,
caches translator/detector instances, download-progress monitor).
Pure lang-code helpers (normalize/sameLanguage/curated targets) with
unit tests.
- Settings: translateTargetLang (default English) + autoTranslate
(opt-in), with a Messages settings tile — a target-language select
and an auto-translate switch, disabled with a note where unsupported.
- useMessageTranslation hook + shared per-event toggle atom-family and a
persisted LRU cache so scrollback never re-translates.
- UI: a Translate / Show Original message-menu action, an inline
"Translated from <lang> - Show original" chip, and a body swap in
m.text/m.emote/m.notice that renders the translated text through the
plain-text path (linkify + emoji) inside a dir=auto span for RTL.
- Auto-translate flips foreign messages whose model is already
downloaded; first-time downloads keep the manual chip (user gesture).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>