Added ajvLocale option

docs/usage-i18n.md

@@ -0,0 +1,64 @@
+---
+title: ▪️ ajvLocale (i18n)
+---
+
+Localizes AJV validation error messages using [ajv-i18n](https://github.com/ajv-validator/ajv-i18n).
+
+!!! Option-schema
+    ```javascript
+    ajvLocale: '<locale>' | (() => '<locale>' | undefined)
+    ```
+
+## ajvLocale (optional)
+
+- `string` – a static locale key applied to every request (e.g. `'de'`, `'ru'`, `'zh'`).
+- `() => string | undefined` – a function called on every validation failure. Return a locale key to translate errors, or `undefined` / an unrecognised key to fall back to English.
+- `undefined` (**default**) – no translation; errors are returned in English.
+
+Supported locale keys: `ar`, `ca`, `cs`, `de`, `en`, `es`, `fi`, `fr`, `hu`, `id`, `it`, `ja`, `ko`, `nb`, `nl`, `pl`, `pt-BR`, `ru`, `sk`, `sv`, `th`, `tr`, `uk`, `vi`, `zh`.
+
+---
+
+### Static locale
+
+All validation errors are translated into the specified language.
+
+```javascript
+app.use(
+  OpenApiValidator.middleware({
+    apiSpec: './openapi.yaml',
+    ajvLocale: 'de', // German error messages
+  }),
+);
+```
+
+---
+
+### Dynamic locale (per-request)
+
+Pass a function to resolve the locale at the time the error occurs. This works with any request-scoped mechanism such as Node's built-in `AsyncLocalStorage`:
+
+```javascript
+import { AsyncLocalStorage } from 'async_hooks';
+
+const localeStorage = new AsyncLocalStorage();
+
+// Upstream middleware – store the locale for the current request
+app.use((req, res, next) => {
+  const lang = req.headers['accept-language']?.split(',')[0]?.trim() ?? 'en';
+  localeStorage.run(lang, next);
+});
+
+app.use(
+  OpenApiValidator.middleware({
+    apiSpec: './openapi.yaml',
+    ajvLocale: () => localeStorage.getStore(), // called fresh on every request
+  }),
+);
+```
+
+---
+
+### Behaviour for unknown or missing locales
+
+If the locale key is not recognised by `ajv-i18n` (e.g. `'xx-UNKNOWN'`), or if the function returns `undefined`, errors are returned in English without throwing.

docs/usage-options-summary.md

@@ -43,5 +43,6 @@ OpenApiValidator.middleware({
   $refParser: {
     mode: 'bundle'
   },
+  ajvLocale: 'de' | (() => 'de' | undefined),
 });
 ```

mkdocs.yml

@@ -60,6 +60,7 @@ nav:
       - usage-file-uploader.md
       - usage-ref-parser.md
       - usage-coerce-types.md
+      - usage-i18n.md
 
   - Guides:
     - Standard API Server: guide-standard.md