From d24ee0a448b044003a92ab20ad9de65dbdf5e5dc Mon Sep 17 00:00:00 2001
From: Ku6epXBOCTuK <Ku6epXBOCTuK@gmail.com>
Date: Mon, 14 Sep 2026 07:39:19 +0500
Subject: [PATCH] chore: add i18n dict consistency lint rule

---
 docs/backlog.md                               |   2 +-
 web/eslint-plugins/README.md                  |  33 +-
 .../__fixtures__/src/lib/i18n/de.ts           |  24 ++
 .../__fixtures__/src/lib/i18n/dict.ts         |  16 +
 .../__fixtures__/src/lib/i18n/en.ts           |  24 ++
 .../__fixtures__/src/lib/i18n/ru.ts           |  24 ++
 .../__tests__/dict-consistency.test.ts        | 146 ++++++++
 web/eslint-plugins/i18n/dict-consistency.js   | 341 ++++++++++++++++++
 web/eslint-plugins/i18n/index.js              |  20 +
 web/eslint.config.js                          |  21 +-
 10 files changed, 648 insertions(+), 3 deletions(-)
 create mode 100644 web/eslint-plugins/__fixtures__/src/lib/i18n/de.ts
 create mode 100644 web/eslint-plugins/__fixtures__/src/lib/i18n/dict.ts
 create mode 100644 web/eslint-plugins/__fixtures__/src/lib/i18n/en.ts
 create mode 100644 web/eslint-plugins/__fixtures__/src/lib/i18n/ru.ts
 create mode 100644 web/eslint-plugins/__tests__/dict-consistency.test.ts
 create mode 100644 web/eslint-plugins/i18n/dict-consistency.js
 create mode 100644 web/eslint-plugins/i18n/index.js

diff --git a/docs/backlog.md b/docs/backlog.md
index 8fbb7b7..de0f0d4 100644
--- a/docs/backlog.md
+++ b/docs/backlog.md
@@ -2,7 +2,7 @@
 
 ## lint и прочие правила
 
-- [ ] Кросс-языковой линтер словарей (warn-only: паритет ключей, пустые
+- [x] Кросс-языковой линтер словарей (warn-only: паритет ключей, пустые
       значения, совпадение `{placeholder}`-переменных между всеми локалями) —
       правило `i18n/dict-consistency`, детали в §Фаза 8
       `docs/plan-preview-i18n.md`
diff --git a/web/eslint-plugins/README.md b/web/eslint-plugins/README.md
index 4a8c9fc..d4a0b40 100644
--- a/web/eslint-plugins/README.md
+++ b/web/eslint-plugins/README.md
@@ -9,9 +9,11 @@
 - `web/eslint-plugins/` — локальные ESLint-плагины.
   - `design-tokens/` — правила для `<style>`-блоков svelte-компонентов.
   - `isolation/` — правило изоляции old/new UI.
+  - `conventions/` — конвенции кода (интерфейс пропсов, запрет union-алиасов).
+  - `i18n/` — кросс-языковой линтер словарей (`dict-consistency`).
   - `__tests__/` — юнит-тесты (Vitest + `RuleTester`/`Linter`).
   - `__fixtures__/` — фикстуры для тестов: миниатюрный `src/app.css` (словарь
-    токенов) и файлы для изоляционных тестов.
+    токенов), файлы для изоляционных тестов и мини-словари `lib/i18n/`.
 - `web/scripts/`:
   - `lint-all.mjs` — оркестратор `lint:all`.
   - `check-tokens.mjs` + `token-audit/` — токен-аудит по `app.css`.
@@ -62,6 +64,35 @@
 (ESLint лезет в `<style>`-блоки через постпрефес postcss AST от
 `svelte-eslint-parser`; stylelint прогоняется по всем CSS-файлам.)
 
+## Правило плагина i18n (`i18n/dict-consistency`)
+
+Кросс-языковой линтер словарей `lib/i18n/` (план: `docs/plan-preview-i18n.md`
+§Фаза 8). Сравнивает каждый словарь со **всеми** остальными локалями (не только
+с BASE). Список локалей берётся из `LOCALES` в `lib/i18n/dict.ts` — новый
+словарь подхватывается без правки правила.
+
+- **warn-only, никогда `error`** — пропущенный перевод не валит сборку.
+- Диагностика живёт там, где фикс: каждый файл репортит **только свои**
+  расхождения:
+  - **паритет ключей**: правило собирает union всех ключей из словарей-соседей
+    (с диска) и для текущего файла репортит те, которых в нём нет — ровно одно
+    предупреждение на разрыв, независимо от числа локалей, где ключ есть;
+    пропавшая целая секция репортится один раз (не по каждому потомку);
+  - **пустые значения**: `""` и строка из одних пробелов;
+  - **паритет плейсхолдеров**: у одинакового ключа набор `{name}` сравнивается с
+    каноническим (мажоритарный по локалям, при равенстве — первый по `LOCALES`)
+    — ловит потерянную при переводе переменную ровно один раз, даже когда
+    отклоняется одна-единственная локаль.
+- Словари-соседи читаются с диска и кэшируются на процесс линта (как
+  `no-undefined-in-svelte`); каждый парсится `@typescript-eslint/parser`
+  (синтакс, без типов).
+- Опция `allowPaths: string[]` — dot-path ключи, исключаемые из всех проверок
+  (осознанные отклонения до достижения zero-warn).
+- Тесты: `__tests__/dict-consistency.test.ts`, фикстуры-словари в
+  `__fixtures__/src/lib/i18n/` (`en`, `ru`, `de` — консистентные, zero-warn) — в
+  тестах подаются модифицированные варианты `en.ts`/`ru.ts` против эталонных на
+  диске.
+
 ## Токены-префиксы (целевой словарь дизайна)
 
 - Цвета: `--color-*`, бренд `--brand-main` / `--brand-alt` — единственные две
diff --git a/web/eslint-plugins/__fixtures__/src/lib/i18n/de.ts b/web/eslint-plugins/__fixtures__/src/lib/i18n/de.ts
new file mode 100644
index 0000000..9d1927d
--- /dev/null
+++ b/web/eslint-plugins/__fixtures__/src/lib/i18n/de.ts
@@ -0,0 +1,24 @@
+import type { Dict } from "./dict";
+
+export const de: Dict = {
+	header: {
+		workspace: "Arbeitsbereich",
+		catalog: "Katalog",
+	},
+	home: {
+		hero: "Hallo {name}!",
+		restoreLast: "{title} wiederherstellen",
+	},
+	errors: {
+		sourceRequired: "Quelle erforderlich",
+	},
+	tools: {
+		addBorder: {
+			title: "Rahmen hinzufügen",
+			description: "Zeichnet einen {kind}-Rahmen.",
+			results: {
+				done: "Rahmen {what}",
+			},
+		},
+	},
+};
diff --git a/web/eslint-plugins/__fixtures__/src/lib/i18n/dict.ts b/web/eslint-plugins/__fixtures__/src/lib/i18n/dict.ts
new file mode 100644
index 0000000..358ebed
--- /dev/null
+++ b/web/eslint-plugins/__fixtures__/src/lib/i18n/dict.ts
@@ -0,0 +1,16 @@
+export const LOCALES = ["en", "ru", "de"] as const;
+
+export const BASE_LOCALE: "en" = "en";
+
+export type Dict = {
+	header: Record<string, string>;
+	home: Record<string, string>;
+	errors: Record<string, string>;
+	tools: Record<string, ToolStrings>;
+};
+
+export type ToolStrings = {
+	title?: string;
+	description?: string;
+	results?: Record<string, string>;
+};
diff --git a/web/eslint-plugins/__fixtures__/src/lib/i18n/en.ts b/web/eslint-plugins/__fixtures__/src/lib/i18n/en.ts
new file mode 100644
index 0000000..e827a95
--- /dev/null
+++ b/web/eslint-plugins/__fixtures__/src/lib/i18n/en.ts
@@ -0,0 +1,24 @@
+import type { Dict } from "./dict";
+
+export const en: Dict = {
+	header: {
+		workspace: "Workspace",
+		catalog: "Catalog",
+	},
+	home: {
+		hero: "Hello {name}!",
+		restoreLast: "Restore {title}",
+	},
+	errors: {
+		sourceRequired: "Source image required",
+	},
+	tools: {
+		addBorder: {
+			title: "Add border",
+			description: "Draws a {kind} frame.",
+			results: {
+				done: "Border {what}",
+			},
+		},
+	},
+};
diff --git a/web/eslint-plugins/__fixtures__/src/lib/i18n/ru.ts b/web/eslint-plugins/__fixtures__/src/lib/i18n/ru.ts
new file mode 100644
index 0000000..05cbf2b
--- /dev/null
+++ b/web/eslint-plugins/__fixtures__/src/lib/i18n/ru.ts
@@ -0,0 +1,24 @@
+import type { Dict } from "./dict";
+
+export const ru: Dict = {
+	header: {
+		workspace: "Рабочая область",
+		catalog: "Каталог",
+	},
+	home: {
+		hero: "Привет, {name}!",
+		restoreLast: "Вернуть {title}",
+	},
+	errors: {
+		sourceRequired: "Нужен исходник",
+	},
+	tools: {
+		addBorder: {
+			title: "Добавить рамку",
+			description: "Рисует рамку {kind}.",
+			results: {
+				done: "Рамка {what}",
+			},
+		},
+	},
+};
diff --git a/web/eslint-plugins/__tests__/dict-consistency.test.ts b/web/eslint-plugins/__tests__/dict-consistency.test.ts
new file mode 100644
index 0000000..4924bbe
--- /dev/null
+++ b/web/eslint-plugins/__tests__/dict-consistency.test.ts
@@ -0,0 +1,146 @@
+// Tests for i18n/dict-consistency (web/eslint-plugins/i18n/dict-consistency.js).
+//
+// The rule reads its own dict dir from disk (LOCALES in dict.ts + sibling
+// locale files), so it runs through the Linter API with cwd pinned to the
+// fixture tree (see __tests__/helpers.ts). The committed fixtures at
+// __fixtures__/src/lib/i18n/ are mutually consistent (zero-warn) — tests feed
+// MODIFIED variants of en.ts / ru.ts as the linted code so each check is
+// exercised against the on-disk references.
+//
+// Reporting contract: each file reports only its OWN gaps. A key missing in a
+// file produces exactly ONE `missingKey` warning, emitted on the incomplete
+// file itself (the union of all keys comes from the on-disk dicts), regardless
+// of how many other locales have the key. Placeholder parity is compared
+// against the canonical set — the one shared by the most locales (ties by
+// LOCALES order) — so a deviation is reported exactly once.
+import fs from "node:fs";
+import path from "node:path";
+import { describe, expect, it } from "vitest";
+import tseslint from "typescript-eslint";
+import dictConsistency from "../i18n/dict-consistency.js";
+import {
+	asRuleModule,
+	FIXTURES_SRC,
+	verifyInFixtures,
+	type FlatConfig,
+} from "./helpers.js";
+
+const I18N_DIR = path.join(FIXTURES_SRC, "lib", "i18n");
+
+const fixture = (name: string) =>
+	fs.readFileSync(path.join(I18N_DIR, name), "utf8");
+
+function lint(code: string, relFile: string, options?: unknown) {
+	const rule = options ? ["warn", options] : "warn";
+	const config: FlatConfig = [
+		{ files: ["**/*.ts"], languageOptions: { parser: tseslint.parser } },
+		{
+			files: ["**/*.ts"],
+			plugins: {
+				i18n: {
+					rules: { "dict-consistency": asRuleModule(dictConsistency) },
+				},
+			},
+			rules: { "i18n/dict-consistency": rule as "warn" },
+		},
+	];
+	return verifyInFixtures(config, code, relFile);
+}
+
+function messageIds(messages: { messageId?: string }[]) {
+	return messages.map((m) => m.messageId);
+}
+
+describe("i18n/dict-consistency", () => {
+	it("stays clean on the consistent fixture dicts", () => {
+		expect(messageIds(lint(fixture("en.ts"), "lib/i18n/en.ts"))).toEqual([]);
+		expect(messageIds(lint(fixture("ru.ts"), "lib/i18n/ru.ts"))).toEqual([]);
+		expect(messageIds(lint(fixture("de.ts"), "lib/i18n/de.ts"))).toEqual([]);
+	});
+
+	it("flags a leaf key missing in the current file", () => {
+		const enMissing = fixture("en.ts").replace(
+			'\t\trestoreLast: "Restore {title}",',
+			"",
+		);
+		const messages = lint(enMissing, "lib/i18n/en.ts");
+		expect(messages).toHaveLength(1);
+		expect(messageIds(messages)).toEqual(["missingKey"]);
+		expect(messages[0].message).toContain('"home.restoreLast"');
+		expect(messages[0].message).toContain(" in en");
+	});
+
+	it("reports a missing whole section once, not per child key", () => {
+		const enNoHeader = fixture("en.ts").replace(/\theader: \{[\s\S]*?\},/, "");
+		const messages = lint(enNoHeader, "lib/i18n/en.ts");
+		expect(messageIds(messages)).toEqual(["missingKey"]);
+		expect(messages[0].message).toContain('"header"');
+		expect(messages[0].message).not.toContain("header.workspace");
+	});
+
+	it("emits ONE warning per gap even when several locales own the key", () => {
+		const enMissing = fixture("en.ts").replace(
+			'\t\tsourceRequired: "Source image required",',
+			"",
+		);
+		const messages = lint(enMissing, "lib/i18n/en.ts");
+		expect(messages).toHaveLength(1);
+		expect(messageIds(messages)).toEqual(["missingKey"]);
+		expect(messages[0].message).toContain('"errors.sourceRequired"');
+		expect(messages[0].message).toContain(" in en");
+	});
+
+	it("flags empty and whitespace-only values", () => {
+		const enEmpty = fixture("en.ts")
+			.replace('workspace: "Workspace",', 'workspace: "",')
+			.replace('catalog: "Catalog",', 'catalog: "   ",');
+		const messages = lint(enEmpty, "lib/i18n/en.ts");
+		expect(messageIds(messages)).toEqual(["emptyValue", "emptyValue"]);
+		expect(messages[0].message).toContain('"header.workspace"');
+		expect(messages[0].message).toContain(" in en");
+		expect(messages[1].message).toContain('"header.catalog"');
+	});
+
+	it("flags a placeholder lost in translation (vs the canonical set)", () => {
+		const ruLostPlaceholder = fixture("ru.ts").replace(
+			'hero: "Привет, {name}!",',
+			'hero: "Привет!",',
+		);
+		const messages = lint(ruLostPlaceholder, "lib/i18n/ru.ts");
+		expect(messages).toHaveLength(1);
+		expect(messageIds(messages)).toEqual(["placeholderMismatch"]);
+		expect(messages[0].message).toContain('"home.hero"');
+		expect(messages[0].message).toContain("{} vs expected {name}");
+	});
+
+	it("flags an extra placeholder introduced in one locale", () => {
+		const enExtraPlaceholder = fixture("en.ts").replace(
+			'description: "Draws a {kind} frame.",',
+			'description: "Draws a {kind} frame by {author}.",',
+		);
+		const messages = lint(enExtraPlaceholder, "lib/i18n/en.ts");
+		expect(messages).toHaveLength(1);
+		expect(messageIds(messages)).toEqual(["placeholderMismatch"]);
+		expect(messages[0].message).toContain('"tools.addBorder.description"');
+		expect(messages[0].message).toContain("{author, kind} vs expected {kind}");
+	});
+
+	it("honours allowPaths for conscious deviations", () => {
+		const enMissing = fixture("en.ts").replace(
+			'\t\tsourceRequired: "Source image required",',
+			"",
+		);
+		const messages = lint(enMissing, "lib/i18n/en.ts", {
+			allowPaths: ["errors.sourceRequired"],
+		});
+		expect(messageIds(messages)).toEqual([]);
+	});
+
+	it("ignores files that are not locale dicts", () => {
+		const notALocale = `
+			export const helper = { a: "b" };
+		`;
+		expect(messageIds(lint(notALocale, "lib/i18n/t.ts"))).toEqual([]);
+		expect(messageIds(lint(notALocale, "lib/i18n/misc.ts"))).toEqual([]);
+	});
+});
diff --git a/web/eslint-plugins/i18n/dict-consistency.js b/web/eslint-plugins/i18n/dict-consistency.js
new file mode 100644
index 0000000..07d4888
--- /dev/null
+++ b/web/eslint-plugins/i18n/dict-consistency.js
@@ -0,0 +1,341 @@
+/**
+ * Cross-locale dictionary linter (i18n/dict-consistency).
+ *
+ * Each locale dict in `lib/i18n/` is checked against ALL the others (not just
+ * against the base locale). The set of locales comes from `LOCALES` in the
+ * sibling `dict.ts`, so a new locale is picked up automatically — no rule
+ * changes needed. The rule only ever warns (a missing translation must not
+ * break the build) — see docs/plan-preview-i18n.md §Фаза 8.
+ *
+ * The diagnostic lives where the fix lives — each file reports its OWN gaps:
+ *   - missing keys: the union of all keys is collected from the on-disk dicts;
+ *     whatever the current file lacks is reported here (a missing whole
+ *     section is reported once, not per descendant key);
+ *   - empty values:  `""` or whitespace-only values;
+ *   - placeholders:  for a shared key the `{name}` set is compared against the
+ *     canonical set (the one shared by most locales, ties broken by LOCALES
+ *     order) — catches a variable lost in translation exactly once, even when
+ *     only one locale deviates.
+ *
+ * The rule self-filters: files whose basename is not one of LOCALES are
+ * ignored, so it can be attached to the whole `lib/i18n/` directory.
+ *
+ * Options (object, all optional):
+ *   - allowPaths: dot-path keys excluded from every check (conscious
+ *     deviations until the dict reaches zero-warn, see Фаза 8 §8.3).
+ */
+import fs from "node:fs";
+import path from "node:path";
+import tseslint from "typescript-eslint";
+
+const PLACEHOLDER = /\{(\w+)\}/g;
+
+/** Parse a TS source string into an ESTree Program (syntax only). */
+function parseTs(code, filename) {
+	const result = tseslint.parser.parseForESLint(code, {
+		filePath: filename,
+		ecmaVersion: "latest",
+		sourceType: "module",
+	});
+	return result.ast;
+}
+
+/** Unwrap `as const` / `satisfies` wrappers around a value node. */
+function unwrap(node) {
+	while (
+		node &&
+		(node.type === "TSAsExpression" || node.type === "TSSatisfiesExpression")
+	) {
+		node = node.expression;
+	}
+	return node;
+}
+
+/**
+ * The exported dict `export const <name>: Dict = {...}` — the declarator id
+ * (for reporting) and the object literal, or null.
+ */
+function findDictExport(ast) {
+	for (const node of ast.body) {
+		if (node.type !== "ExportNamedDeclaration") continue;
+		const decl = node.declaration;
+		if (!decl || decl.type !== "VariableDeclaration") continue;
+		const d = decl.declarations[0];
+		if (!d || d.id.type !== "Identifier") continue;
+		const init = unwrap(d.init);
+		if (init && init.type === "ObjectExpression") {
+			return { id: d.id, object: init };
+		}
+	}
+	return null;
+}
+
+/** The `LOCALES` list exported from `dict.ts`, or null. */
+function findLocalesList(ast) {
+	for (const node of ast.body) {
+		if (node.type !== "ExportNamedDeclaration") continue;
+		const decl = node.declaration;
+		if (!decl || decl.type !== "VariableDeclaration") continue;
+		for (const d of decl.declarations) {
+			if (d.id.type !== "Identifier" || d.id.name !== "LOCALES") continue;
+			const init = unwrap(d.init);
+			if (init && init.type === "ArrayExpression") {
+				return init.elements
+					.map((el) => (isStringLiteral(el) ? el.value : null))
+					.filter((v) => typeof v === "string");
+			}
+		}
+	}
+	return null;
+}
+
+/**
+ * String literal node. The parser emits `Literal` in some ESTree versions and
+ * `StringLiteral` in others — accept both.
+ */
+function isStringLiteral(node) {
+	if (!node) return false;
+	if (node.type === "StringLiteral") return true;
+	return node.type === "Literal" && typeof node.value === "string";
+}
+
+const OBJECT = "object";
+const STRING = "string";
+const OPAQUE = "opaque";
+
+/** Leaf kind of a property value (objects are followed, the rest are opaque). */
+function entryKind(node) {
+	if (node.type === "ObjectExpression") return OBJECT;
+	if (isStringLiteral(node)) return STRING;
+	if (
+		node.type === "TemplateLiteral" &&
+		node.expressions.length === 0 &&
+		node.quasis.length === 1
+	) {
+		return STRING;
+	}
+	return OPAQUE;
+}
+
+function entryValue(node) {
+	if (isStringLiteral(node)) return node.value;
+	if (node.type === "TemplateLiteral") return node.quasis[0].value.cooked;
+	return null;
+}
+
+function propKey(prop) {
+	if (prop.key.type === "Identifier") return prop.key.name;
+	if (isStringLiteral(prop.key)) return prop.key.value;
+	return null;
+}
+
+/**
+ * Flatten an exported dict object into `path -> { node, kind, value }`.
+ * Computed properties are skipped; intermediate objects are recorded too, so a
+ * missing whole section is reported once (children of a missing path are
+ * skipped when reporting).
+ */
+function buildKeyMap(objectNode) {
+	const map = new Map();
+	const stack = [[objectNode, []]];
+	while (stack.length > 0) {
+		const [obj, prefix] = stack.pop();
+		for (const prop of obj.properties) {
+			if (prop.type !== "Property" || prop.computed) continue;
+			const key = propKey(prop);
+			if (key == null) continue;
+			const dot = [...prefix, key].join(".");
+			const kind = entryKind(prop.value);
+			map.set(dot, {
+				node: prop,
+				kind,
+				value: kind === STRING ? entryValue(prop.value) : null,
+			});
+			if (kind === OBJECT) stack.push([prop.value, [...prefix, key]]);
+		}
+	}
+	return map;
+}
+
+function placeholders(value) {
+	const set = new Set();
+	for (const m of String(value).matchAll(PLACEHOLDER)) set.add(m[1]);
+	return set;
+}
+
+function formatSet(set) {
+	return `{${[...set].sort().join(", ")}}`;
+}
+
+/** Ancestor paths of a dot-path (e.g. `a.b` and `a` for `a.b.c`). */
+function* ancestorPaths(key) {
+	let i = key.lastIndexOf(".");
+	while (i !== -1) {
+		yield key.slice(0, i);
+		i = key.lastIndexOf(".", i - 1);
+	}
+}
+
+// Sibling dicts are read once per directory and cached for the whole lint run
+// (mirrors how no-undefined-in-svelte caches the token dictionary).
+const dirCache = new Map();
+
+function loadDir(dir) {
+	if (!dirCache.has(dir)) dirCache.set(dir, readDir(dir));
+	return dirCache.get(dir);
+}
+
+function readDir(dir) {
+	const dictPath = path.join(dir, "dict.ts");
+	if (!fs.existsSync(dictPath)) return null;
+	const ast = parseTs(fs.readFileSync(dictPath, "utf8"), dictPath);
+	const locales = findLocalesList(ast);
+	if (!locales || locales.length === 0) return null;
+
+	const dicts = [];
+	for (const locale of locales) {
+		const file = path.join(dir, `${locale}.ts`);
+		if (!fs.existsSync(file)) {
+			// Declared in LOCALES but not yet translated — treated as an empty
+			// dict so every key it lacks reports `missing key ... in <locale>`.
+			dicts.push({ locale, map: new Map() });
+			continue;
+		}
+		const dictAst = parseTs(fs.readFileSync(file, "utf8"), file);
+		const dictExport = findDictExport(dictAst);
+		if (!dictExport) continue;
+		dicts.push({ locale, map: buildKeyMap(dictExport.object) });
+	}
+
+	// Union of every key across all locales (intermediate paths included), so a
+	// file can report exactly what it is missing.
+	const unionPaths = new Set();
+	// Non-empty string leaves per key: loccales contribute to the canonical
+	// placeholder set voting (empty values are already broken on their own).
+	const stringLeaves = new Map();
+	for (const d of dicts) {
+		for (const [key, entry] of d.map) {
+			unionPaths.add(key);
+			if (entry.kind === STRING && (entry.value ?? "").trim() !== "") {
+				if (!stringLeaves.has(key)) stringLeaves.set(key, []);
+				stringLeaves.get(key).push(placeholders(entry.value));
+			}
+		}
+	}
+
+	// Canonical placeholder set per key: the set shared by the most locales;
+	// on a tie the first one encountered (LOCALES order) wins.
+	const canonicalSets = new Map();
+	for (const [key, sets] of stringLeaves) {
+		const counts = new Map();
+		for (const set of sets) {
+			const sig = [...set].sort().join("\u0000");
+			counts.set(sig, (counts.get(sig) || 0) + 1);
+		}
+		let bestCount = 0;
+		for (const set of sets) {
+			const sig = [...set].sort().join("\u0000");
+			if (counts.get(sig) > bestCount) {
+				bestCount = counts.get(sig);
+				canonicalSets.set(key, set);
+			}
+		}
+	}
+
+	return { locales, dicts, unionPaths, canonicalSets };
+}
+
+export default {
+	meta: {
+		type: "suggestion",
+		docs: {
+			description:
+				"Check cross-locale consistency of the i18n dicts in lib/i18n (warn-only).",
+			category: "Best Practices",
+		},
+		schema: [
+			{
+				type: "object",
+				properties: {
+					allowPaths: {
+						type: "array",
+						items: { type: "string" },
+					},
+				},
+				additionalProperties: false,
+			},
+		],
+		messages: {
+			missingKey: 'missing key "{{key}}" in {{locale}}',
+			emptyValue: 'empty value "{{key}}" in {{locale}}',
+			placeholderMismatch:
+				'placeholder mismatch for "{{key}}" in {{locale}}: {{active}} vs expected {{expected}}',
+		},
+	},
+	create(context) {
+		const options = context.options[0] || {};
+		const allowPaths = new Set(options.allowPaths || []);
+
+		const filename = path.resolve(
+			context.filename || context.physicalFilename || "",
+		);
+		const locale = path.basename(filename, path.extname(filename));
+		const dirInfo = loadDir(path.dirname(filename));
+		if (!dirInfo || !dirInfo.locales.includes(locale)) return {};
+
+		const dictExport = findDictExport(context.sourceCode.ast);
+		if (!dictExport) return {};
+
+		const own = buildKeyMap(dictExport.object);
+
+		// Missing keys: everything the union has but the current file lacks.
+		// Top-level gaps only — a missing ancestor already covers its subtree.
+		const missing = [...dirInfo.unionPaths].filter((k) => !own.has(k));
+		const missingSet = new Set(missing);
+		const topMissing = missing.filter(
+			(k) => ![...ancestorPaths(k)].some((a) => missingSet.has(a)),
+		);
+		for (const key of topMissing) {
+			if (allowPaths.has(key)) continue;
+			context.report({
+				node: dictExport.id,
+				messageId: "missingKey",
+				data: { key, locale },
+			});
+		}
+
+		// Empty values and shared-key placeholder parity.
+		for (const [key, entry] of own) {
+			if (allowPaths.has(key) || entry.kind !== STRING) continue;
+			if ((entry.value ?? "").trim() === "") {
+				context.report({
+					node: entry.node,
+					messageId: "emptyValue",
+					data: { key, locale },
+				});
+				continue;
+			}
+			const canonical = dirInfo.canonicalSets.get(key);
+			if (!canonical) continue;
+			const active = placeholders(entry.value);
+			if (
+				active.size === canonical.size &&
+				[...active].every((p) => canonical.has(p))
+			) {
+				continue;
+			}
+			context.report({
+				node: entry.node,
+				messageId: "placeholderMismatch",
+				data: {
+					key,
+					locale,
+					active: formatSet(active),
+					expected: formatSet(canonical),
+				},
+			});
+		}
+
+		return {};
+	},
+};
diff --git a/web/eslint-plugins/i18n/index.js b/web/eslint-plugins/i18n/index.js
new file mode 100644
index 0000000..49f8868
--- /dev/null
+++ b/web/eslint-plugins/i18n/index.js
@@ -0,0 +1,20 @@
+/**
+ * Local ESLint plugin "i18n".
+ *
+ * Cross-locale dictionary hygiene (i18n/dict-consistency): every locale dict in
+ * `lib/i18n/` is compared against all the others — key parity, empty values,
+ * `{placeholder}` parity — warn-only by design (a missing translation must not
+ * break the build). The set of locales comes from `LOCALES` in `dict.ts`, so
+ * new locales are picked up automatically.
+ */
+import dictConsistency from "./dict-consistency.js";
+
+export default {
+	meta: {
+		name: "i18n",
+		version: "0.1.0",
+	},
+	rules: {
+		"dict-consistency": dictConsistency,
+	},
+};
diff --git a/web/eslint.config.js b/web/eslint.config.js
index 10cdf6f..ad91c67 100644
--- a/web/eslint.config.js
+++ b/web/eslint.config.js
@@ -7,6 +7,7 @@ import tseslint from "typescript-eslint";
 import designTokens from "./eslint-plugins/index.js";
 import isolationPlugin from "./eslint-plugins/isolation/index.js";
 import conventionsPlugin from "./eslint-plugins/conventions/index.js";
+import i18nPlugin from "./eslint-plugins/i18n/index.js";
 
 // FIXME: надо игнорировать старые файлы, после переноса пути новых компонентов включают старые
 // Новый код редизайна: к нему применяем полные recommended-наборы уже сейчас.
@@ -82,6 +83,11 @@ export default tseslint.config(
 						"eslint-plugins/__tests__/no-string-union-alias.test.ts",
 						"eslint-plugins/__tests__/helpers.ts",
 						"eslint-plugins/__tests__/no-mixed-imports.test.ts",
+						"eslint-plugins/__tests__/dict-consistency.test.ts",
+						"eslint-plugins/__fixtures__/src/lib/i18n/dict.ts",
+						"eslint-plugins/__fixtures__/src/lib/i18n/en.ts",
+						"eslint-plugins/__fixtures__/src/lib/i18n/ru.ts",
+						"eslint-plugins/__fixtures__/src/lib/i18n/de.ts",
 						"eslint-plugins/__fixtures__/src/lib/v1/old.ts",
 						"eslint-plugins/__fixtures__/src/lib/v1/i18n/t.ts",
 						"eslint-plugins/__fixtures__/src/lib/core/errors.ts",
@@ -92,7 +98,7 @@ export default tseslint.config(
 						"eslint-plugins/__fixtures__/src/routes/+page.svelte",
 						"eslint-plugins/__fixtures__/src/routes/v1/+layout.svelte",
 					],
-					maximumDefaultProjectFileMatchCount_THIS_WILL_SLOW_DOWN_LINTING: 32,
+					maximumDefaultProjectFileMatchCount_THIS_WILL_SLOW_DOWN_LINTING: 40,
 				},
 				extraFileExtensions: [".svelte"],
 			},
@@ -168,6 +174,19 @@ export default tseslint.config(
 			"conventions/no-string-union-alias": "error",
 		},
 	},
+	// Кросс-языковой линтер словарей (плагин i18n/dict-consistency).
+	// warn-only: пропущенный перевод не должен валить сборку. Список локалей
+	// берётся из LOCALES в lib/i18n/dict.ts — новые локали подхватываются
+	// автоматически; правило игнорирует не-локали в этой папке само.
+	{
+		files: ["**/src/lib/i18n/*.ts"],
+		plugins: {
+			i18n: i18nPlugin,
+		},
+		rules: {
+			"i18n/dict-consistency": "warn",
+		},
+	},
 	// Полные recommended-наборы — только на новый код.
 	...[
 		...jsRecommended.map((cfg) => ({