Walks en.json in order (top-level + nested).
For each leaf key:
- Keeps the locale's existing translation if present.
- Otherwise pulls the translation from tools/i18n/patches/<lang>.json (a flat object keyed by dotted path).
- If neither exists, leaves the key absent and exits non-zero.
Writes the merged tree back to the locale file with 4-space indent and a trailing newline.

Existing translations are never overwritten.

Workflow

# 1. Generate one missing-strings dump per locale (flat dotted-path → EN string)
node tools/i18n/fill-missing.mjs --emit-missing
# → tools/i18n/missing/<lang>.json

# 2. Translate each missing/<lang>.json into the equivalent patch file
#    in tools/i18n/patches/<lang>.json (same shape: { dotted.path: translated }).

# 3. Merge patches into the locale files
node tools/i18n/fill-missing.mjs

# 4. Verify
node -e "
const fs=require('fs');
const en=JSON.parse(fs.readFileSync('apps/web/src/assets/i18n/en.json','utf8'));
const collect=(d,p='')=>Object.entries(d).flatMap(([k,v])=>v&&typeof v==='object'?collect(v,p?p+'.'+k:k):[p?p+'.'+k:k]);
const enKeys=new Set(collect(en));
for(const f of fs.readdirSync('apps/web/src/assets/i18n').filter(x=>x.endsWith('.json')&&x!=='en.json')){
  const k=new Set(collect(JSON.parse(fs.readFileSync('apps/web/src/assets/i18n/'+f,'utf8'))));
  console.log(f,'missing:',[...enKeys].filter(x=>!k.has(x)).length,'extra:',[...k].filter(x=>!enKeys.has(x)).length);
}"

For a non-mutating CI/agent check, run:

pnpm run i18n:check

The check fails on missing or extra keys against en.json, and on values that are identical to English unless identical-en-baseline.json lists that exact English text for the locale and key. Do not copy English into a locale as a placeholder: translate it. The contract, including when an entry stops covering a key, is in the validation map.

Baseline entries that are no longer identical are reported, not fatal. After translating baselined values, or for a value that is legitimately the same in a language (a brand, a technical name, a loanword), rewrite the baseline and review every added entry in the diff:

pnpm run i18n:baseline:update

The checker's own tests run with pnpm run i18n:test; CI runs both through pnpm run i18n:validate. For a full audit that ignores the baseline, run:

node tools/i18n/check-drift.mjs --fail-on-identical

Translation rules

Preserve {{interpolation}} placeholders verbatim.
Preserve any inline HTML tags.
Match the locale's existing punctuation, casing, and terminology.
Keep brand names (IPTVnator, Xtream, Stalker, M3U, EPG, MPV, VLC) untranslated.
Short UI strings stay short — no length blow-up.