A mistake is either intentionally or unintentionally deviant and self corrigible. Slips or lapses of the tongue, pen, or keyboard are easily detected and can be self corrected by their author unaided.
While learning a language everybody make mistakes, from infants in their native tongue to everyone else, either very young or adult, wanting to somehow communicate in a language different from their mother tongue.Making mistakes while learning (not only a language) is probably in-born in human beings (and in animals, too), so that if we want to learn something we need to be trained and corrected till the aim is attained, since “we learn from our mistakes”, as the old saying goes.