I would have been so happy if a foreigner could speak even 10% of my mother tongue. Well of course they don't have to as it's not required. But I guess since English is the worldwide accepted official language in almost all countries we all make an effort to at least talk and write at a level that the other person at least manages to understand something. Many of us may not write exactly in the way native English-speaking people write because we didn't speak English from birth. Nor did we go to schools that taught English at that level. Even in our workplaces or daily businesses, English is just another language that most of us only use rarely. Some of us who read and write more may be better than others but most of us are not at that level yet because we haven't practiced at that level.