I was surprised to learn that one roughly quarter of ESL teachers in the US are not native speakers of English. They may be just as good at teaching as the native speakers. However,  if I emigrated to China or Poland, I would certainly prefer to learn the local language from a Chinese or Polish teacher, rather than an American or French teacher.  I wonder how many students who travel to a country to learn a language would happily accept a non-native speaker as a language teacher. Surprised.