Desktop app v1.18286.0 launched in Spanish on an English-only macOS system

After auto-updating to 1.18286.0 (app bundle replaced 2 Jul 07:35), the Claude desktop app UI rendered entirely in Spanish — sidebar, settings, input bar, notification toasts.

Environment

• macOS 25.5.0 (Darwin), Apple Silicon
• System is single-language: AppleLanguages = (en-GB), AppleLocale = en_GB — no Spanish anywhere in preferred languages
• Desktop app version 1.18286.0

Expected: UI in English, matching the system locale.
Actual: Entire UI chrome in Spanish. Model responses unaffected (English).

Notes

• There is no in-app display-language setting — Settings → General → "Idioma" is the voice dictation language only, so it can't be fixed from inside the app.
• Workaround: macOS per-app language override (System Settings → General → Language & Region → Applications → + → Claude → English), then relaunch. The app then renders in English (US) — presumably en-US is the only English localization shipped, so en-GB falls back to it.

Clean repro case since the system has no Spanish configured at all — suggests the update's locale detection defaulted to es rather than reading the system language.