ADR 0183: P0 international shell locales

• Status: Accepted
• Date: 2026-09-08
• Decision owners: PI-Desktop desktop/i18n maintainers
• Related: ADR 0160, ADR 0182, D346, E2E-091

Context

The locale registry could add languages without renderer-specific picker work, but the shipped shell stopped at English, Simplified Chinese, Traditional Chinese, and Turkish. Spanish, French, and German are high-value international locales for the desktop product and were missing from the UI catalog and in-app release notes.

Decision

1. Ship complete shell catalogs for de, es, and fr, keeping English as the source catalog and preserving key and interpolation parity.
2. Register native names Deutsch, Español, and Français; the searchable picker continues to derive its options from the shared locale registry.
3. Resolve de-*, es-*, and fr-* OS locale tags to their shipped base catalogs. Persisted AppSettings.language accepts the three new ids.
4. Ship matching product changelog catalogs so release notes follow the active locale. No host protocol, storage schema, or Electron IPC version changes.

Consequences

• Users can select German, Spanish, or French without a renderer reload.
• Locale parity tests cover shell strings, both interpolation styles, and release-note version/highlight parity.
• Regional variants intentionally share one base catalog; region-specific spelling can be added later without changing the picker contract.

Alternatives

• Add only registry rows and fall back to English: rejected because it would advertise languages without localizing the shell.
• Add region-specific catalogs immediately: rejected because the P0 goal is broad coverage with one maintainable catalog per language.