What should I write for the code in middleware 'detect_user_locale_middleware'

[adnanerlansyah403]

What is this error mean?

{
    "message": "RequestValidator is not defined",
    "name": "ReferenceError",
    "status": 500,
    "frames": [
        {
            "file": "app/middleware/detect_user_locale_middleware.ts",
            "filePath": "d:/allproject/personal/api/warung-buneng/app/middleware/detect_user_locale_middleware.ts",
            "line": 4,
            "callee": "Function.<static_initializer>",
            "calleeShort": "<static_initializer>",
            "column": 9,
            "context": {
                "start": 1,
                "pre": "\nexport default class DetectUserLocaleMiddleware {\n    static {",
                "line": "        RequestValidator.messagesProvider = (ctx) => {",
                "post": "          return ctx.i18n.createMessagesProvider()\n        }\n    }\n  }\n  "
            },
            "isModule": false,
            "isNative": false,
            "isApp": true
        },
        {
            "file": "app/middleware/detect_user_locale_middleware.ts",
            "filePath": "d:/allproject/personal/api/warung-buneng/app/middleware/detect_user_locale_middleware.ts",
            "line": 2,
            "callee": "<anonymous>",
            "calleeShort": "<anonymous>",
            "column": 1,
            "context": {
                "start": 1,
                "pre": "",
                "line": "export default class DetectUserLocaleMiddleware {",
                "post": "    static {\n        RequestValidator.messagesProvider = (ctx) => {\n          return ctx.i18n.createMessagesProvider()\n        }\n    }"
            },
            "isModule": false,
            "isNative": false,
            "isApp": true
        },
        {
            "file": "node:internal/modules/esm/module_job",
            "filePath": "node:internal/modules/esm/module_job",
            "line": 218,
            "callee": "ModuleJob.run",
            "calleeShort": "run",
            "column": 25,
            "context": {},
            "isModule": false,
            "isNative": false,
            "isApp": false
        },
        {
            "file": "node:internal/modules/esm/loader",
            "filePath": "node:internal/modules/esm/loader",
            "line": 329,
            "callee": "async ModuleLoader.import",
            "calleeShort": "import",
            "column": 24,
            "context": {},
            "isModule": false,
            "isNative": false,
            "isApp": false
        },
        {
            "file": "node_modules/@poppinss/utils/src/import_default.ts",
            "filePath": "D:/allproject/personal/api/warung-buneng/node_modules/@poppinss/utils/src/import_default.ts",
            "line": 19,
            "callee": "importDefault",
            "calleeShort": "importDefault",
            "column": 25,
            "context": {},
            "isModule": true,
            "isNative": false,
            "isApp": false
        },
        {
            "file": "node_modules/@adonisjs/fold/src/module_importer.ts",
            "filePath": "D:/allproject/personal/api/warung-buneng/node_modules/@adonisjs/fold/src/module_importer.ts",
            "line": 157,
            "callee": "Object.handle",
            "calleeShort": "handle",
            "column": 29,
            "context": {},
            "isModule": true,
            "isNative": false,
            "isApp": false
        }
    ]
}

Even though I've been already following the instruction from this documentation to be activate the middleware to detect the locale of user:
https://docs.adonisjs.com/guides/i18n#translating-validation-messages

Where does the RequestValidator come from? is it an instance of class or what?