Even in a non-native speaker they are still signs of poor comprehension. If you are going to have someone write your documentation, they had better know the language. I have not bought from some companies a second time because their documentation was so bad.

And, truthfully, many non-native writers are as good as many natives. Non-native speakers can be more readily identified (if for some reason you want to) through unusual word choices or stilted (overly formal) grammar.