According to my little experience on italki, I think not every native speaker of a specific language is able to teach this language. We should consider several points such as: Firstly, his/her skills to deliver the information and the correct pronunciation. Secondly, his/her knowledge of the language. Thirdly, the techniques which he/she can use to teach. Finally, how much motivated he/she is to spend much time teaching his/her language partner. For these reason, I believe that not all people can be a language partner to teach me their language. I don't generalize, it is just my perspective.

Not everyone, the people involved have to be reasonably proficient in their own languages and there has to be a good connection and rapport between the two people.

i know but i mean that the people who can speak english learn the othears to speak it and who can speak arabic learn who want to speak it   but my english is not good to say that