@@ -0,0 +1,12 @@
+---
+"@objectstack/plugin-audit": minor
+---
+
+`AuditPluginOptions` gains `getLocale`, an optional host locale resolver asked before the settings-derived locale, so a multi-organization host can write each organization's activity summaries in its language
+
+Clause-②: yes (widening)
+
+- **The option.** `new AuditPlugin({ getLocale })`, where `getLocale` is `(tenantId?: string, userId?: string) => string | undefined | Promise<string | undefined>`. It picks the language of `sys_activity.summary` and of the @mention notification title the plugin emits, and is called with the write's organization and user (for an @mention title, the mentioned recipient).
+- **Precedence: host first, settings second.** An answer that is a well-formed BCP-47 tag is used, in its canonical form (`zh-cn` → `zh-CN`). `undefined`, `null` or a blank string falls back to the settings-derived `localization.locale` (ADR-0053) the plugin used before this option. So do a malformed answer (`zh_CN`, a non-string) and a throw or rejected promise; each of those two faults is logged once at `warn`, and neither fails the audited write. There is no other locale source.
+- **Without the option, nothing changes.** The settings-derived locale stays the only source, as before.
+- The locale only picks the message catalog, and a summary is rendered once, when its row is written. Rows already written keep their text.
@@ -42,8 +42,7 @@ await kernel.use(
 );
 ```
 
-`readAudit` is the only key `AuditPluginOptions` declares, and it accepts
-exactly those three:
+`readAudit` accepts exactly those three:
 
 | Key | Default | Meaning |
 | --- | --- | --- |
@@ -59,6 +58,10 @@ object** rather than silently accepted. An empty — or fully excluded — set
 registers no hook, so a deployment that opts nothing in pays nothing on its read
 path.
 
+`AuditPluginOptions` declares one other key, `getLocale`, a host locale resolver
+for the language activity summaries are written in; it does not change what is
+audited.
+
 <Callout type="warn">
 **There is no object-metadata key and no environment variable.** `enable.auditReads`
 does not exist, and neither does a global "audit all reads" flag. The shape is
 
@@ -37,8 +37,8 @@ await kernel.use(new AuditPlugin());
 ```
 
 Write coverage is not configured per object — see
-[Coverage](#coverage-subtraction-not-an-allow-list). The one thing that *is* configured is
-**record-view auditing**, which records nothing until objects are named:
+[Coverage](#coverage-subtraction-not-an-allow-list). Of what gets recorded, the one thing that
+*is* configured is **record-view auditing**, which records nothing until objects are named:
 
 ```typescript
 await kernel.use(
@@ -48,8 +48,9 @@ await kernel.use(
 );
 ```
 
-`readAudit` is the only key `AuditPluginOptions` declares, and it accepts exactly three
-settings, no others:
+`AuditPluginOptions` declares two keys: `readAudit`, and `getLocale` (the language activity
+summaries are written in — [below](#activity-summary-language--getlocale)). `readAudit`
+accepts exactly three settings, no others:
 
 | Option | Default | Meaning |
 |---|---|---|
@@ -61,6 +62,36 @@ settings, no others:
 plugin does **not** forward. Setting it requires calling `installReadAuditWriter` directly
 against the engine; there is no plugin-level spelling for it.
 
+### Activity summary language — `getLocale`
+
+`sys_activity.summary` and the @mention notification title are written in one language,
+chosen per write. Without options it is the deployment's settings-derived
+`localization.locale` (ADR-0053). A host that knows better per organization passes a
+resolver, which is asked first with the write's `tenantId` and `userId` (for an @mention
+title, the mentioned recipient):
+
+```typescript
+await kernel.use(
+  new AuditPlugin({
+    // (tenantId?: string, userId?: string) => string | undefined | Promise<string | undefined>
+    getLocale: async (tenantId) => organizationLocale(tenantId),
+  }),
+);
+```
+
+| The resolver… | The write's locale |
+|---|---|
+| answers a well-formed BCP-47 tag | that tag, canonicalized (`zh-cn` → `zh-CN`) |
+| answers `undefined`, `null` or a blank string | the settings-derived locale |
+| answers a malformed tag (`zh_CN`) or a non-string | the settings-derived locale, logged once at `warn` |
+| throws, or its promise rejects | the settings-derived locale, logged once at `warn` with the error; the audited write still lands |
+
+Precedence is host first, settings second, and there is no third source. The writer memoizes
+the answer per tenant/user scope for a short TTL, so a resolver may read its own storage
+directly. The locale only picks the message catalog: one the i18n service has no catalog for
+degrades the way a settings-derived locale does, to the service's declared fallback and then to
+the English literal. A summary is rendered once, when the row is written.
+
 The plugin depends on the ObjectQL engine (`com.objectstack.engine.objectql`) and resolves
 it at `kernel:ready`. If no engine is available it logs a warning and installs no writers.
 
 
@@ -0,0 +1,251 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+import { describe, it, expect } from 'vitest';
+// STATIC on purpose, like audit-writers.test.ts: the plugin's own kernel:ready
+// hook imports the translation bundle lazily, and a static import here moves
+// that cold-start cost to collection, which no test's timeout is charged for.
+import { createMemoryI18n } from '@objectstack/core';
+import { AuditTranslations } from './translations/index.js';
+import { AuditPlugin, type AuditPluginOptions } from './audit-plugin.js';
+
+/**
+ * `AuditPluginOptions.getLocale` — the host locale resolver, driven through the
+ * PLUGIN (init → start → kernel:ready), not through `installAuditWriters`
+ * directly: the option is only worth anything if the plugin really hands it to
+ * the writers ahead of the settings-derived locale it builds itself.
+ *
+ * The settings service answers `ja-JP` throughout, so every outcome is
+ * distinguishable: the host's locale (zh-CN), the settings fallback (ja-JP),
+ * and the English literal a locale-less write degrades to.
+ */
+
+interface CapturedRow {
+  object: string;
+  row: Record<string, any>;
+}
+
+/** A fake ObjectQL engine: records hooks (honouring `object` / `excludeObjects`) and created rows. */
+function makeEngine() {
+  const hooks = new Map<string, Array<{ fn: (ctx: any) => any; opts: any }>>();
+  const created: CapturedRow[] = [];
+  const api = {
+    sudo: () => ({
+      object(name: string) {
+        return {
+          async create(row: Record<string, any>) {
+            created.push({ object: name, row });
+            return { id: `${name}-${created.length}`, ...row };
+          },
+        };
+      },
+    }),
+  };
+  const schemas: Record<string, Record<string, any>> = {
+    sys_audit_log: { name: 'sys_audit_log', fields: {} },
+    sys_activity: { name: 'sys_activity', fields: {} },
+    person_qualification: {
+      name: 'person_qualification',
+      label: 'Qualification',
+      fields: { id: { type: 'text' }, name: { type: 'text' } },
+    },
+  };
+  for (const f of ['id', 'action', 'user_id', 'actor', 'object_name', 'record_id', 'old_value', 'new_value', 'tenant_id']) {
+    schemas.sys_audit_log.fields[f] = { type: 'text' };
+  }
+  for (const f of ['id', 'type', 'timestamp', 'summary', 'actor_id', 'object_name', 'record_id', 'record_label', 'metadata']) {
+    schemas.sys_activity.fields[f] = { type: 'text' };
+  }
+  const engine = {
+    getSchema(name: string) {
+      return schemas[name];
+    },
+    registerHook(event: string, fn: (ctx: any) => any, opts?: any) {
+      const list = hooks.get(event) ?? [];
+      list.push({ fn, opts: opts ?? {} });
+      hooks.set(event, list);
+    },
+    unregisterHooksByPackage() {
+      /* no-op */
+    },
+  };
+  async function fire(event: string, ctx: any) {
+    for (const { fn, opts } of hooks.get(event) ?? []) {
+      if (opts.object && opts.object !== ctx.object) continue;
+      if (Array.isArray(opts.excludeObjects) && opts.excludeObjects.includes(ctx.object)) continue;
+      await fn({ ...ctx, event, api });
+    }
+  }
+  return { engine, fire, created };
+}
+
+/** A settings occupant whose `localization.locale` is `ja-JP` (the fallback every case can see). */
+function makeSettings(locale = 'ja-JP') {
+  const values: Record<string, unknown> = { locale };
+  return {
+    // `resolveLocalizationContext` takes the settings path only when `get` exists, then prefers `getMany`.
+    async get(_ns: string, key: string) {
+      return values[key] === undefined ? undefined : { value: values[key] };
+    },
+    async getMany(_ns: string, keys: string[]) {
+      return Object.fromEntries(keys.map((k) => [k, values[k] === undefined ? undefined : { value: values[k] }]));
+    },
+  };
+}
+
+async function boot(options?: AuditPluginOptions, services: { settings?: unknown } = { settings: makeSettings() }) {
+  const { engine, fire, created } = makeEngine();
+  const i18n = createMemoryI18n();
+  for (const [locale, data] of Object.entries(AuditTranslations)) {
+    i18n.loadTranslations(locale, data as Record<string, unknown>);
+  }
+  const registry = new Map<string, unknown>([
+    ['objectql', engine],
+    ['manifest', { register() {} }],
+    ['i18n', i18n],
+  ]);
+  if (services.settings !== undefined) registry.set('settings', services.settings);
+  const readyHooks: Array<() => Promise<void> | void> = [];
+  const warns: Array<{ msg: string; meta?: Record<string, unknown> }> = [];
+  const logger = {
+    info() {},
+    warn(msg: string, meta?: Record<string, unknown>) {
+      warns.push({ msg: String(msg), meta });
+    },
+    error() {},
+    debug() {},
+    child() {
+      return logger;
+    },
+  };
+  const ctx = {
+    logger,
+    getService(name: string) {
+      return registry.get(name);
+    },
+    registerService(name: string, svc: unknown) {
+      registry.set(name, svc);
+    },
+    hook(event: string, fn: () => Promise<void> | void) {
+      if (event === 'kernel:ready') readyHooks.push(fn);
+    },
+  } as any;
+  const plugin = options === undefined ? new AuditPlugin() : new AuditPlugin(options);
+  await plugin.init(ctx);
+  await plugin.start(ctx);
+  for (const fn of readyHooks) await fn();
+
+  const insert = (tenant = 'org-1', user = 'user-1', name = 'OC-00001') =>
+    fire('afterInsert', {
+      object: 'person_qualification',
+      input: { id: `q-${name}` },
+      result: { id: `q-${name}`, name },
+      session: { organizationId: tenant, userId: user },
+    });
+  const summaries = () => created.filter((c) => c.object === 'sys_activity').map((c) => c.row.summary);
+  const localeWarns = () => warns.filter((w) => w.msg.includes('getLocale'));
+  return { insert, summaries, created, localeWarns };
+}
+
+const ZH = '创建了 Qualification "OC-00001"';
+const JA = 'Qualification「OC-00001」を作成しました';
+const EN = 'Created Qualification "OC-00001"';
+
+describe('AuditPlugin — host locale resolver (AuditPluginOptions.getLocale)', () => {
+  it('pin: a create on a tracked object writes sys_activity.summary in the resolver\'s locale', async () => {
+    const calls: Array<[string | undefined, string | undefined]> = [];
+    const { insert, summaries, localeWarns } = await boot({
+      getLocale: async (tenantId, userId) => {
+        calls.push([tenantId, userId]);
+        return 'zh-CN';
+      },
+    });
+    await insert();
+    expect(summaries()).toEqual([ZH]);
+    // Asked with the write's organization and user, ahead of the settings read.
+    expect(calls).toEqual([['org-1', 'user-1']]);
+    expect(localeWarns()).toEqual([]);
+  });
+
+  it('a synchronous answer counts, and is used in its canonical form', async () => {
+    const { insert, summaries } = await boot({ getLocale: () => ' zh-cn ' });
+    await insert();
+    expect(summaries()).toEqual([ZH]);
+  });
+
+  it('fallback: a resolver answering undefined gives today\'s settings-derived locale', async () => {
+    const { insert, summaries, localeWarns } = await boot({ getLocale: async () => undefined });
+    await insert();
+    expect(summaries()).toEqual([JA]);
+    expect(localeWarns()).toEqual([]);
+  });
+
+  it('fallback: null and a blank string are "no answer" too, silently', async () => {
+    const asNull = await boot({ getLocale: (async () => null) as unknown as AuditPluginOptions['getLocale'] });
+    await asNull.insert();
+    expect(asNull.summaries()).toEqual([JA]);
+    expect(asNull.localeWarns()).toEqual([]);
+
+    const blank = await boot({ getLocale: () => '   ' });
+    await blank.insert();
+    expect(blank.summaries()).toEqual([JA]);
+    expect(blank.localeWarns()).toEqual([]);
+  });
+
+  it('absent: with no option the summary is the settings-derived one (the existing-behaviour control)', async () => {
+    const withSettings = await boot();
+    await withSettings.insert();
+    expect(withSettings.summaries()).toEqual([JA]);
+
+    // An options bag without the member is the same as no bag at all.
+    const emptyBag = await boot({});
+    await emptyBag.insert();
+    expect(emptyBag.summaries()).toEqual([JA]);
+
+    // And no settings service either: the built-in en-US default — English.
+    const bare = await boot(undefined, {});
+    await bare.insert();
+    expect(bare.summaries()).toEqual([EN]);
+  });
+
+  it('throw: falls through to the settings-derived locale, logged once at warn with the error, and the write lands', async () => {
+    let calls = 0;
+    const { insert, summaries, created, localeWarns } = await boot({
+      getLocale: () => {
+        calls += 1;
+        throw new Error('locale store unreachable');
+      },
+    });
+    await insert('org-1', 'user-1', 'OC-00001');
+    // A second scope asks again (the writer memoizes per tenant/user) and throws again.
+    await insert('org-2', 'user-2', 'OC-00002');
+    expect(calls).toBe(2);
+    expect(summaries()).toEqual([JA, 'Qualification「OC-00002」を作成しました']);
+    // The audited write is not failed by the host's fault: both ledger rows landed.
+    expect(created.filter((c) => c.object === 'sys_audit_log')).toHaveLength(2);
+    const warned = localeWarns();
+    expect(warned).toHaveLength(1);
+    expect(warned[0].msg).toMatch(/host getLocale resolver threw/);
+    expect(warned[0].meta).toEqual({ err: 'locale store unreachable' });
+  });
+
+  it('throw: a rejected promise falls through the same way', async () => {
+    const { insert, summaries, localeWarns } = await boot({
+      getLocale: () => Promise.reject(new Error('timeout')),
+    });
+    await insert();
+    expect(summaries()).toEqual([JA]);
+    expect(localeWarns()).toHaveLength(1);
+    expect(localeWarns()[0].meta).toEqual({ err: 'timeout' });
+  });
+
+  it('an answer that is not a well-formed BCP-47 tag falls back, logged once at warn', async () => {
+    const { insert, summaries, localeWarns } = await boot({ getLocale: () => 'zh_CN' });
+    await insert('org-1', 'user-1', 'OC-00001');
+    await insert('org-2', 'user-2', 'OC-00002');
+    expect(summaries()).toEqual([JA, 'Qualification「OC-00002」を作成しました']);
+    const warned = localeWarns();
+    expect(warned).toHaveLength(1);
+    expect(warned[0].msg).toContain('"zh_CN"');
+    expect(warned[0].msg).toMatch(/not a well-formed BCP-47 locale tag/);
+  });
+});