diff --git a/docs/i18n/ADAPTIVE_CURRENT_STATE_REPORT_v3.md b/docs/i18n/ADAPTIVE_CURRENT_STATE_REPORT_v3.md
new file mode 100644
index 00000000..3c8ed34a
--- /dev/null
+++ b/docs/i18n/ADAPTIVE_CURRENT_STATE_REPORT_v3.md
@@ -0,0 +1,139 @@
+# Adaptive Current-State Report v3 — i18n hardening + LanguageTool editor integration
+
+> **Mandatory Phase-0 deliverable** for the "i18n hardening + 5 new locales + real LanguageTool"
+> program. This is read-only ground truth captured before any feature code, so the work *extends* the
+> existing system rather than reinventing it. Status fields below are accurate as of **2026-06-24**.
+
+## 1. Locale inventory (SSOT: `i18n/locales.ts`)
+
+19 locales, each a typed `LocaleDescriptor` in the single source of truth. The `.mjs`
+build/check/translate scripts derive their list from the `locales/<code>/` folders; the
+`tests/unit/i18n/localesRegistry.test.ts` integrity guard asserts the two never drift.
+
+| Tier | Locales | Notes |
+|------|---------|-------|
+| **Production** (5) | de, en, es, fr, **it** | full key parity + translated `help.json` (`helpFallback: false`) |
+| **Near-Production** (4) | ja, zh, pt, el | ≥96% UI coverage, 0 placeholder issues; `help.json` still English-fallback |
+| **Beta** (10) | ar, he (RTL); fi, sv, hu, is, eu; fa (RTL); ru, ko | UI coverage varies; `help.json` English-fallback |
+
+`status` drives the README badge + `LanguageSelector` β-badge (`isBeta` = the *beta* tier specifically,
+so Near-Production is distinguished from Beta). RTL = ar/he/fa. Scripts: latin/arabic/hebrew/cjk/
+greek/cyrillic/hangul (font wiring per script; Korean needs Noto Sans KR via CDN, Cyrillic self-hosts).
+
+## 2. LanguageTool reality — scaffold only, NOT a working grammar checker
+
+- **`services/languageToolClient.ts`** is a **gate + connectivity ping**, nothing more:
+  - `assertLanguageToolAllowed(settings, baseUrl)` — throws if the LT integration is disabled, the URL
+    is invalid, or `privacy.localStorageOnly` is on **and** the host is not `localhost`/`127.0.0.1`
+    (privacy-first: remote LT blocked in local-only mode).
+  - `languageToolPing(baseUrl, sampleText)` — a single `POST /v2/check` with `language=en-US` that
+    returns `res.ok`. **It does not parse `matches[]`, does not surface issues, and is hardcoded to
+    English.** No real grammar checking exists anywhere in the editor.
+- **The Writer "grammar check" is unrelated** — `hooks/useWriterView.ts` `grammarCheck` is an
+  **AI/Gemini prompt**, not LanguageTool.
+- **Settings surface already exists**: `components/settings/IntegrationsSection.tsx` renders the
+  LanguageTool card; settings shape is `integrations.languageToolEnabled` (default **false**) +
+  `integrations.languageToolBaseUrl` (default `http://localhost:8010`). This is the scaffold PR-C
+  builds on — no new Settings plumbing required for enable/baseURL.
+
+## 3. Editor seam for inline underlines (`components/manuscript/ManuscriptEditor.tsx`)
+
+The editor is a **plain `<textarea>` with an aligned highlight overlay** — an `absolute inset-0 …
+pointer-events-none overflow-auto` layer that renders the same text with the **exact same font stack**
+as the textarea so glyphs stay aligned (it already powers search-term highlights and is RTL-aware).
+**LanguageTool underlines reuse this exact technique**: map LT match `offset`/`length` → overlay spans
+with an underline decoration; a hover/click popover (PR-C2) hangs off those spans. No new editor
+architecture is needed — only a second overlay decoration source.
+
+## 4. Existing docs / tooling to extend (do NOT duplicate)
+
+- `docs/i18n/`: `ADDING_A_NEW_LANGUAGE.md`, `BETA_TO_PRODUCTION_PLAYBOOK.md`, `BETA_QUALITY_AUDIT.md`,
+  `TRANSLATION_STATUS.md`, `AUDIT_AND_IMPROVEMENT_PLAN.md`, `BETA_COMPLETION_LOG.md`, `IMPLEMENTATION_LOG.md`.
+- `docs/`: `I18N-GLOSSARY.md`, `TRANSLATION-GUIDE.md`, `LANGUAGE-EXPANSION-2026.md`, `BULK-TRANSLATION.md`.
+- `scripts/bulk-translate-locales.mjs` (glossary-anchored, placeholder-masked, `--dry-run`),
+  `check-i18n-keys.mjs`, `build-i18n.mjs`, `i18n-locales.mjs`.
+
+The 5 new locales route through `ADDING_A_NEW_LANGUAGE.md` + `bulk-translate-locales.mjs`; tier
+decisions extend `TRANSLATION_STATUS.md` (see the Review & Elevation Log added there) rather than a new
+file.
+
+## 5. **Verified LanguageTool support matrix** (dev.languagetool.org/languages, 2026-06-24)
+
+This is the load-bearing correction to the original plan. Tiers below are now encoded in
+`i18n/locales.ts` as `languageToolSupport` (`strong` | `partial` | `none`) + `languageToolCode`.
+
+| Locale | LT rules / spell | Tier in registry | LT code |
+|--------|------------------|------------------|---------|
+| en | 6074 + spell | **strong** | en-US |
+| fr | 6984 + spell | **strong** | fr |
+| de | 5224 + spell | **strong** | de-DE |
+| pt | 2919 + spell | **strong** | pt-PT |
+| es | 1644 + spell | **strong** | es |
+| nl *(new)* | 3500 + spell | **strong** | nl |
+| pl *(new)* | 1747 + spell | **strong** | pl-PL |
+| uk *(new)* | 1186 + spell | **strong** | uk-UA |
+| zh | 1863, no spell | partial | zh-CN |
+| ru | 892 + spell, unmaintained | partial | ru-RU |
+| ja | 735, no spell | partial | ja-JP |
+| ro *(new)* | 457 + spell | partial | ro-RO |
+| ar | 450 + spell | partial | ar |
+| fa | 283, no spell | partial | fa |
+| it | 141 + spell | partial | it |
+| el | 55 + spell | partial | el-GR |
+| sv | 32 + spell | partial | sv |
+| **tr** *(new)* | **NOT supported** | **none** | — |
+| he, fi, hu, is, eu, ko | **NOT supported** | **none** | — |
+
+### ⚠ Material finding — Turkish has NO LanguageTool support
+The original plan asserted "pl/nl/tr/uk/ro all have strong LanguageTool coverage." **That is false for
+Turkish** — Turkish is absent from LanguageTool's supported-languages list entirely. Decision:
+- Turkish **stays** in the 5-locale Workstream-A set — its value is creative-writing UI demand, which
+  is independent of grammar checking. It is added as a normal Beta UI locale.
+- Turkish gets `languageToolSupport: 'none'` → the grammar feature is simply **absent** for `tr`, the
+  same honest treatment as he/fi/hu/is/eu/ko. No fake grammar promise.
+- Of the 5 new locales, **pl/nl/uk = strong, ro = partial, tr = none**. The LT feature therefore lands
+  meaningfully for 4 of the 5.
+
+## 6. Adjusted prioritization
+
+- **Workstream B (registry enrichment) — done in this PR.** `languageToolSupport` + `languageToolCode`
+  added to all 19 entries (verified data), with `getLanguageToolCode()` / `hasLanguageToolSupport()`
+  SSOT helpers so the editor feature gates on one source. Integrity test extended.
+- **Workstream C (real LanguageTool) — primary.** MVP "Check this scene" panel (PR-C1) → live inline
+  overlay (PR-C2). Self-hosted only; the existing `assertLanguageToolAllowed` privacy gate stays. The
+  locale→LT code map is `getLanguageToolCode()`; `none` locales hide the feature.
+- **Workstream A (5 locales) — pl, nl, tr, uk, ro**, one stacked PR each, via the existing pipeline.
+  `pt-BR` and Chinese variants are deferred → `ROADMAP.md`.
+
+## 7. Tier elevation posture (honest, data-gated)
+
+No tier is promoted in this PR. Promotion (near-production → production) requires translated `help.json`
+(the single gap for ja/zh/pt/el) **plus** parity + 0 placeholder-integrity issues — recorded
+per-decision in the **Review & Elevation Log** appended to `docs/i18n/TRANSLATION_STATUS.md`. Beta
+labels stay until the data supports otherwise; we do not over-promote.
+
+## 8. Risks / anti-patterns (and mitigations)
+
+- **Over-promising grammar** for unsupported locales → mitigated: `none` tier hides the feature; the
+  registry test pins he/fi/hu/is/eu/ko (+tr) to `none`.
+- **Cloud LT leaking private prose** → mitigated: `assertLanguageToolAllowed` keeps remote LT blocked
+  under local-only privacy mode; self-hosted (`localhost:8010`) is the documented default.
+- **Editor perf regression from live checking** → mitigated (PR-C2): debounce, active/visible section
+  only, cancel in-flight on keystroke, MVP-first.
+- **English on Beta surfaces** (CodeAnt/review custom rule rejects it) → mitigated: translate new
+  user-visible strings up front (core-5 by hand, Beta via bulk-translate); `help.json` stays
+  English-fallback for Beta by policy (tag-dense HTML is not safely MT-able).
+- **Locale fan-out crossing ~100 files** (review bot skips) → mitigated: one locale per PR.
+- **Registry drift** → mitigated: `languageToolCode` present **iff** support ≠ `none`, asserted by the
+  integrity test.
+
+## 9. Deliverable status (this PR = Phase-0 + Workstream B)
+
+- [x] This report.
+- [x] `i18n/locales.ts` enriched (LT support + code, helpers) + integrity test extended.
+- [x] Review & Elevation Log seeded in `docs/i18n/TRANSLATION_STATUS.md`.
+- [ ] Glossary anchor terms for the 5 new locales — added per-locale when each lands (Workstream A),
+      where the bulk-translate context is concrete.
+- [ ] `languageToolService` + PR-C1/C2 — next PR.
+- [ ] 5 locale additions — subsequent stacked PRs.
+- [ ] LanguageTool Integration Architecture doc + ADR + final handover report — closing PR.
diff --git a/docs/i18n/TRANSLATION_STATUS.md b/docs/i18n/TRANSLATION_STATUS.md
index 004cd978..3507cd63 100644
--- a/docs/i18n/TRANSLATION_STATUS.md
+++ b/docs/i18n/TRANSLATION_STATUS.md
@@ -41,3 +41,21 @@ Production: de, en, fr, es, it · Near-Production: ja, zh, pt, el · Beta: ar, h
 > for every non-core locale, plus a native pass over UI microcopy. See
 > [`BETA_TO_PRODUCTION_PLAYBOOK.md`](./BETA_TO_PRODUCTION_PLAYBOOK.md).
 
+## Review & Elevation Log
+
+Append-only record of every tier decision (and the data behind it), so promotions are auditable and we
+never over-promote without evidence. See
+[`ADAPTIVE_CURRENT_STATE_REPORT_v3.md`](./ADAPTIVE_CURRENT_STATE_REPORT_v3.md) for the program context.
+
+| Date | Locale | Tier | Decision | Basis |
+|------|--------|------|----------|-------|
+| 2026-06-24 | ja, zh, pt, el | Near-Production | held | ≥96% UI coverage, 0 placeholder issues; **blocked from Production** solely by English-fallback `help.json` |
+| 2026-06-24 | ar, he, fi, sv, hu, is, eu, fa, ru, ko | Beta | held | translated UI but no native review pass; `help.json` English-fallback |
+| 2026-06-24 | de, en, es, fr, it | Production | held | full parity + native `help.json` |
+
+**LanguageTool coverage** is tracked in `i18n/locales.ts` (`languageToolSupport`) and the
+[Phase-0 report §5](./ADAPTIVE_CURRENT_STATE_REPORT_v3.md#5-verified-languagetool-support-matrix), and
+is **orthogonal** to the translation tier — a Production locale can have weak LT (it: partial) and a
+Beta locale can have strong LT (pl/nl/uk, once added). No promotion in this PR; this log is the seam
+for future, data-gated elevations.
+
diff --git a/i18n/locales.ts b/i18n/locales.ts
index 73718a1c..6d0f6944 100644
--- a/i18n/locales.ts
+++ b/i18n/locales.ts
@@ -5,6 +5,15 @@
 // lists from the filesystem (they cannot import this TS module), and a registry-integrity unit test
 // asserts the two stay in sync.
 
+/**
+ * LanguageTool grammar-coverage tier for a locale (drives the optional in-editor grammar feature).
+ * - `strong`  — large mature rule set + spell check (de/en/fr/es/pt/nl/pl/uk).
+ * - `partial` — supported but limited: low rule count and/or no spell check (it/ru/ja/zh/el/ar/fa/sv/ro).
+ * - `none`    — not supported by LanguageTool at all → the grammar feature is simply absent, honestly
+ *               (tr/fi/hu/is/eu/he/ko). Verified against dev.languagetool.org/languages (2026-06-24).
+ */
+export type LanguageToolSupport = 'strong' | 'partial' | 'none';
+
 /**
  * One locale's display + behaviour metadata.
  * - `nativeName` is the endonym (intentionally NOT localized so users always find their own language).
@@ -12,6 +21,8 @@
  * - `flag` is an emoji (non-translatable); Basque has no flag emoji → globe.
  * - `status` drives the Production / Near-Production / Beta tier surfaced in the UI + README.
  * - `helpFallback` = true when `help.json` long-form content still falls back to English.
+ * - `languageToolSupport` = LanguageTool grammar tier (SSOT for the editor grammar feature's gating).
+ * - `languageToolCode` = the LanguageTool API `language` parameter; present iff support !== 'none'.
  */
 export interface LocaleDescriptor {
   readonly code: string;
@@ -22,6 +33,8 @@ export interface LocaleDescriptor {
   readonly status: 'production' | 'near-production' | 'beta';
   readonly script: 'latin' | 'arabic' | 'hebrew' | 'cjk' | 'greek' | 'cyrillic' | 'hangul';
   readonly helpFallback: boolean;
+  readonly languageToolSupport: LanguageToolSupport;
+  readonly languageToolCode?: string;
 }
 
 // QNBS-v3: `as const` keeps each `code` a string literal so `Language` stays an exhaustive union
@@ -37,6 +50,8 @@ export const LOCALES = [
     status: 'production',
     script: 'latin',
     helpFallback: false,
+    languageToolSupport: 'strong',
+    languageToolCode: 'de-DE',
   },
   {
     code: 'en',
@@ -47,6 +62,8 @@ export const LOCALES = [
     status: 'production',
     script: 'latin',
     helpFallback: false,
+    languageToolSupport: 'strong',
+    languageToolCode: 'en-US',
   },
   {
     code: 'fr',
@@ -57,6 +74,8 @@ export const LOCALES = [
     status: 'production',
     script: 'latin',
     helpFallback: false,
+    languageToolSupport: 'strong',
+    languageToolCode: 'fr',
   },
   {
     code: 'es',
@@ -67,6 +86,8 @@ export const LOCALES = [
     status: 'production',
     script: 'latin',
     helpFallback: false,
+    languageToolSupport: 'strong',
+    languageToolCode: 'es',
   },
   {
     code: 'it',
@@ -77,6 +98,9 @@ export const LOCALES = [
     status: 'production',
     script: 'latin',
     helpFallback: false,
+    // QNBS-v3: Italian is supported but has a small rule set (~141 XML rules) → partial, not strong.
+    languageToolSupport: 'partial',
+    languageToolCode: 'it',
   },
   // RTL Beta (B-5).
   {
@@ -88,6 +112,8 @@ export const LOCALES = [
     status: 'beta',
     script: 'arabic',
     helpFallback: true,
+    languageToolSupport: 'partial',
+    languageToolCode: 'ar',
   },
   {
     code: 'he',
@@ -98,6 +124,8 @@ export const LOCALES = [
     status: 'beta',
     script: 'hebrew',
     helpFallback: true,
+    // QNBS-v3: Hebrew is not in LanguageTool's supported languages → grammar feature absent.
+    languageToolSupport: 'none',
   },
   // QNBS-v3: Near-Production (PR4) — ≥96% UI string coverage with 0 placeholder-integrity issues
   // (per `pnpm run i18n:report`); help.json still falls back to English (helpFallback: true), which is
@@ -111,6 +139,9 @@ export const LOCALES = [
     status: 'near-production',
     script: 'cjk',
     helpFallback: true,
+    // QNBS-v3: Japanese has rules but no spell check → partial.
+    languageToolSupport: 'partial',
+    languageToolCode: 'ja-JP',
   },
   {
     code: 'zh',
@@ -121,6 +152,9 @@ export const LOCALES = [
     status: 'near-production',
     script: 'cjk',
     helpFallback: true,
+    // QNBS-v3: Chinese has rules but no spell check → partial.
+    languageToolSupport: 'partial',
+    languageToolCode: 'zh-CN',
   },
   {
     code: 'pt',
@@ -131,6 +165,8 @@ export const LOCALES = [
     status: 'near-production',
     script: 'latin',
     helpFallback: true,
+    languageToolSupport: 'strong',
+    languageToolCode: 'pt-PT',
   },
   {
     code: 'el',
@@ -141,6 +177,9 @@ export const LOCALES = [
     status: 'near-production',
     script: 'greek',
     helpFallback: true,
+    // QNBS-v3: Greek is supported but has a very small rule set (~55) → partial.
+    languageToolSupport: 'partial',
+    languageToolCode: 'el-GR',
   },
   // Phase X Beta — Nordic / Uralic / Basque (LTR) + Persian (RTL, Arabic script).
   {
@@ -152,6 +191,8 @@ export const LOCALES = [
     status: 'beta',
     script: 'latin',
     helpFallback: true,
+    // QNBS-v3: Finnish is not in LanguageTool's supported languages → grammar feature absent.
+    languageToolSupport: 'none',
   },
   {
     code: 'sv',
@@ -162,6 +203,9 @@ export const LOCALES = [
     status: 'beta',
     script: 'latin',
     helpFallback: true,
+    // QNBS-v3: Swedish is spell-check + ~32 rules only → partial.
+    languageToolSupport: 'partial',
+    languageToolCode: 'sv',
   },
   {
     code: 'hu',
@@ -172,6 +216,8 @@ export const LOCALES = [
     status: 'beta',
     script: 'latin',
     helpFallback: true,
+    // QNBS-v3: Hungarian is not in LanguageTool's supported languages → grammar feature absent.
+    languageToolSupport: 'none',
   },
   {
     code: 'is',
@@ -182,6 +228,8 @@ export const LOCALES = [
     status: 'beta',
     script: 'latin',
     helpFallback: true,
+    // QNBS-v3: Icelandic is not in LanguageTool's supported languages → grammar feature absent.
+    languageToolSupport: 'none',
   },
   // QNBS-v3: Basque has no Unicode flag emoji (ikurriña absent) → globe.
   {
@@ -193,6 +241,8 @@ export const LOCALES = [
     status: 'beta',
     script: 'latin',
     helpFallback: true,
+    // QNBS-v3: Basque is not in LanguageTool's supported languages → grammar feature absent.
+    languageToolSupport: 'none',
   },
   {
     code: 'fa',
@@ -203,6 +253,9 @@ export const LOCALES = [
     status: 'beta',
     script: 'arabic',
     helpFallback: true,
+    // QNBS-v3: Persian has rules but no spell check → partial.
+    languageToolSupport: 'partial',
+    languageToolCode: 'fa',
   },
   // QNBS-v3: Tier-1 expansion (2026) — Russian (Cyrillic). Inter + Merriweather self-host the
   // Cyrillic subset via @fontsource, so no CDN/`:lang()` font wiring is needed.
@@ -215,6 +268,9 @@ export const LOCALES = [
     status: 'beta',
     script: 'cyrillic',
     helpFallback: true,
+    // QNBS-v3: Russian has ~892 rules + spell but no recent rule maintenance → partial (conservative).
+    languageToolSupport: 'partial',
+    languageToolCode: 'ru-RU',
   },
   // QNBS-v3: Tier-1 expansion (2026) — Korean (Hangul). Inter does NOT cover Hangul, so this needs
   // Noto Sans KR via the Google Fonts CDN (index.html) + a `:lang(ko)` font rule (index.css).
@@ -227,6 +283,8 @@ export const LOCALES = [
     status: 'beta',
     script: 'hangul',
     helpFallback: true,
+    // QNBS-v3: Korean is not in LanguageTool's supported languages → grammar feature absent.
+    languageToolSupport: 'none',
   },
 ] as const satisfies ReadonlyArray<LocaleDescriptor>;
 
@@ -276,3 +334,14 @@ export const getLocaleInfo = (code: Language): LocaleDescriptor | undefined =>
 /** True when `value` is a supported locale code (runtime-safe guard for persisted/URL values). */
 export const isLanguage = (value: unknown): value is Language =>
   typeof value === 'string' && LOCALE_BY_CODE.has(value);
+
+/**
+ * The LanguageTool API `language` code for a locale, or null when LanguageTool does not support it
+ * (the grammar feature must be hidden/disabled for that locale). SSOT for the editor grammar layer.
+ */
+export const getLanguageToolCode = (code: Language): string | null =>
+  LOCALE_BY_CODE.get(code)?.languageToolCode ?? null;
+
+/** True when a locale has any (strong or partial) LanguageTool grammar coverage. */
+export const hasLanguageToolSupport = (code: Language): boolean =>
+  (LOCALE_BY_CODE.get(code)?.languageToolSupport ?? 'none') !== 'none';
diff --git a/tests/unit/i18n/localesRegistry.test.ts b/tests/unit/i18n/localesRegistry.test.ts
index 7ee4e4ae..307d0f24 100644
--- a/tests/unit/i18n/localesRegistry.test.ts
+++ b/tests/unit/i18n/localesRegistry.test.ts
@@ -11,7 +11,9 @@ import { existsSync, readdirSync } from 'node:fs';
 import { join } from 'node:path';
 import { describe, expect, it } from 'vitest';
 import {
+  getLanguageToolCode,
   getLocaleInfo,
+  hasLanguageToolSupport,
   isLanguage,
   LOCALE_CODES,
   LOCALES,
@@ -99,4 +101,40 @@ describe('i18n locale registry (SSOT)', () => {
     expect(en?.status).toBe('production');
     expect(en?.dir).toBe('ltr');
   });
+
+  it('every locale declares a valid LanguageTool support tier', () => {
+    const valid = new Set(['strong', 'partial', 'none']);
+    for (const l of LOCALES) {
+      expect(valid.has(l.languageToolSupport), `${l.code}: ${l.languageToolSupport}`).toBe(true);
+    }
+  });
+
+  it('languageToolCode is present iff the locale has LanguageTool support', () => {
+    // QNBS-v3: SSOT invariant — a usable LT code exists exactly when support !== 'none', so the
+    // editor grammar feature can gate on getLanguageToolCode() returning non-null.
+    for (const l of LOCALES) {
+      // QNBS-v3: read the code via the LocaleDescriptor-typed lookup — the `as const` literal type of
+      // `none` entries omits the optional `languageToolCode`, so direct access there is a type error.
+      const hasCode = Boolean(getLocaleInfo(l.code)?.languageToolCode);
+      const supported = l.languageToolSupport !== 'none';
+      expect(hasCode, `${l.code}: code/support mismatch`).toBe(supported);
+      expect(hasLanguageToolSupport(l.code), l.code).toBe(supported);
+      expect(getLanguageToolCode(l.code) !== null, l.code).toBe(supported);
+    }
+  });
+
+  it('LanguageTool-unsupported locales (verified) expose no grammar feature', () => {
+    // QNBS-v3: verified against dev.languagetool.org/languages (2026-06-24); these must stay 'none'
+    // so we never promise grammar checking we cannot deliver.
+    for (const code of ['he', 'fi', 'hu', 'is', 'eu', 'ko'] as const) {
+      expect(getLocaleInfo(code)?.languageToolSupport, code).toBe('none');
+      expect(getLanguageToolCode(code), code).toBeNull();
+    }
+  });
+
+  it('the core 5 production locales all have LanguageTool coverage', () => {
+    for (const code of ['de', 'en', 'es', 'fr', 'it'] as const) {
+      expect(hasLanguageToolSupport(code), code).toBe(true);
+    }
+  });
 });