Some people believe that if you grow up speaking several languages, you “gain width but lose depth”, i.e. you may be fluent in several languages, but none of the languages you know will be as good as the mother tonge of a monoglot.
Please, how can I translate this concept into Persian?
در حالی که پهنی میبری، ژرفا میبازی.
Best wishes, and many thanks,