Limit field in MapfField

[Odselmaa]

Hello! I have field like this -> translation = MapField(EmbeddedDocumentField(Translation))
I wanna get "ru" field in translation.

       "name": "something.....",
        "translation": {
            "ru": {
                "name": "something......"
            }
        }

I tried ?_fields=translation__ru . But it's not working. Please help me!