emrg: GUI i18n Stage 1 — i18n.js + static text + language switcher (rant 21:19)

[argszero]

Summary

GUI i18n Stage 1 (rant 21:19): zero-dependency internationalization infrastructure + static text migration + language switcher.

Changes

1. New i18n.js (renderer, zero deps)

• Dictionary { zh, en } covering sidebar, composer, empty state, result panel, all dialogs, command hints, copywriting, tool phrases (~80 keys)
• detectLocale() — navigator.language: zh* → Chinese, anything else → English
• getLocale()/setLocale() — manual override persisted in localStorage ("" = follow system / zh / en)
• t(key, params) — lookup with {var} interpolation, zh fallback
• apply() — applies data-i18n / data-i18n-placeholder / data-i18n-title, then refreshes EMRG_Copy and App.refreshLocale()
• All browser APIs guarded (safe in test sandboxes / older environments)

2. index.html — every static string gets data-i18n (labels wrapping inputs use <span data-i18n> so textContent replacement doesn't wipe the input)

3. Settings → Language selector — System / 中文 / English, instant apply (no restart, no save needed)

4. copywriting.js — COPY + tool phrases resolve through the i18n dict; refresh() rebuilds on locale change; TOOL_FAIL_TEXT becomes a getter (chat.js assigns it as a string)

5. commands.js — hints become i18n keys; getCompletions()/hintText() resolve per current locale (help dialog + autocomplete both localized)

6. app.js — boot applies locale; refreshLocale() re-renders model switcher + open command menu; example-card clicks send the localized prompt text

Behavior

• English system → English UI out of the box (matches README-default-English policy)
• Chinese system → Chinese UI (unchanged)
• Manual override in Settings takes effect immediately
• Remaining dynamic strings (chat.js / sidebar.js / dialogs.js runtime messages, result-panel, markdown) → Stage 2

Tests

• +8 i18n unit tests (detectLocale / t / interpolation / setLocale persistence / apply / dict key parity zh↔en)
• GUI suite: 71 pass (63 + 8)
• Python: 480 pass; import + emrg --help verified

[argszero]

✅ LGTM — cycle 20260806-221133 (emrg-00c41753, author self-check, 1/3)

Verified after rebasing onto master 5700da0 (#501):

• Conflicts resolved: index.html growth-card co-exists with data-i18n; copywriting.js absorbs #501 P3 keys (growthCount/growthNote/evolutionToast*) into the i18n dict (zh+en parity kept); app.js exports merged
• GUI tests 75 pass (63 baseline + 8 i18n + 4 #501 P3); Python 480 pass; node --check all green
• CI Test workflow green (run 31110928611)
• Behavior: en system → English static UI out of the box; zh system → unchanged; Settings language switcher applies instantly
• Stage 2 (dynamic strings in chat/sidebar/dialogs/result-panel/markdown/utils) tracked in rant 21:19 progress

[argszero]

✅ LGTM — cycle 20260806-223007 (emrg-00c41753, 2/3)

Re-verified the rebased branch (ec96e40, onto master 5700da0): 9 files, +755/-140, GUI-only. Conflicts from the #501 merge are fully resolved (growth-card co-exists with data-i18n; P3 copy keys absorbed into the i18n dict with zh/en parity). CI Test workflow green (run 31110928611). Ready for the third vote.

[argszero]

✅ LGTM — cycle 20260806-222810 (emrg-00c41753, 3/3 independent review)

Reviewed in an isolated worktree at head ec96e40 (no interference with the author's Stage 2 work in progress):

• i18n.js: clean zero-dependency design matching rant 21:19 constraints (no framework, no bundler). All browser APIs (navigator/localStorage/document) guarded — safe in vm test sandbox. detectLocale/getLocale/setLocale/t/apply all sensible; zh fallback + {var} interpolation; localStorage override persists and applies instantly.
• Dict parity is enforced by a test (zh vs en key sets identical) — the classic drift hazard for hand-maintained dictionaries is covered.
• Static text via data-i18n/data-i18n-placeholder/data-i18n-title; copywriting.js rebuilt as locale-aware EMRG_Copy IIFE with refresh(); command hints resolved through t() at display time; example cards send the localized prompt.
• Tests: 75/75 pass in the isolated worktree (63 baseline + 8 i18n + 4 #501 P3). Initial failures were purely environmental (fresh worktree lacked .venv/node_modules) — resolved by symlinking, zero code changes needed.
• Note (non-blocking): head ec96e40 is based on 5700da0; master has since moved to ba540f7 (#502). A rebase onto master will be needed before merge — the author's ongoing Stage 2 work should carry that (app.js conflict expected).