feat(i18n): add multi-language support for buddy reactions, achievements, and MCP responses

[ndcorder]

Summary

• Adds multi-language (i18n) support for buddy reactions, achievements, and MCP response strings — closes [FEATURE] Add multi language support #16
• Ships 18 locales: en (verified) + 17 AI-translated (zh, es, ja, de, fr, pt, ko, ru, ro, uk, tr, hi, it, pl, vi, ar, th)
• Zero dependencies — custom JSON locale loader with fallback to English for missing keys

What changed

New files:

• server/i18n.ts — zero-dep locale loader (t(), tArray(), tObj(), auto-discovers locale files)
• locales/en.json — 2249-line English base with all Phase 1 strings
• locales/*.json — 17 translated locales, each structurally validated
• server/i18n.test.ts — 36 tests / 17,113 assertions validating all locales
• scripts/translate*.ts — translation + audit tooling for adding new languages

Migrated files:

• server/reactions.ts — all 100 reaction reasons, 18 species pools, stat overrides, escalation tiers, rarity flair now loaded from locale
• server/achievements.ts — 130 achievement names/descriptions rendered via t()
• server/index.ts — MCP response strings migrated, buddy_language tool added
• server/state.ts — language field added to BuddyConfig (default: "en")

CLI/skill updates:

• cli/settings.ts — bun run settings language <code>
• skills/buddy/SKILL.md — /buddy language [code] routing
• cli/index.ts — help text updated
• CONTRIBUTING.md — translation contribution guide
• .gitignore / package.json — i18n.lock ignored, locales/ in files array

How it works

• Locale files live in locales/<code>.json, auto-discovered by scanning the directory
• Each file has _language (display name) and _verified (boolean) metadata fields
• setLocale(code) switches the active locale; t("key") looks up strings with English fallback
• Users switch languages via /buddy language es or bun run settings language ja
• The language picker shows "(AI-generated, unreviewed)" for non-verified locales

Translation quality

• All 17 locales scored GOOD (4.4–5.0) in automated accuracy/tone/naturalness audit
• 0% English fallbacks, 100% placeholder integrity across all locales
• Translated with Claude Sonnet 4 + per-language style guides + few-shot examples
• _verified: false on all AI locales — native speaker review sets it to true

How to test

bun test                    # 282 tests pass (246 existing + 36 new i18n)
bun run settings language   # show current language + available options
/buddy language es          # switch buddy to Spanish in Claude Code

Adding a new language: copy locales/en.json, translate values, drop it in locales/. No code changes needed.

[ndcorder]

I am currently working on iterating the translation quality

[ramarivera]

Hey @ndcorder — triaging the queue after the project's rename (claude-buddy → coding-buddy, native Pi / Oh My Pi extensions, npm publishing). Checking in on this one: it's the biggest open PR by far (17 locales, ~42k lines) and it now conflicts with main — and the gap widens with every merge, since reactions/achievements keep growing (38 new achievements landed since this was opened, plus the extension work).

Honest question before anyone invests more effort: are you still actively iterating on this? If yes, it probably makes sense to re-scope — land the string-extraction/i18n architecture first as a smaller PR, then locales incrementally, so the translation surface stops racing main. If life has moved on (totally fine), we'll close this and turn it into a roadmap issue crediting your groundwork so it isn't lost.

🤖 Created with the help of AI (Claude Fable 5).