There's a reason why interviews are rarely conducted in the interviewee's native language. People end up with poor interviews. It doesn't matter about the translation, that's the easy part. Unless the interviewer is fluent the questions asked are wrong and the interviewer can't understand or respond to anything said, so no follow-up questions can be asked. You try and go up to someone in the street and conduct an interview in French if you don't speak French and they do. It will be a load of sht as you won't know what they're saying or where to take the interview. This is why the interviews are in English because even if the interviewee's English is 'poor' it's way, way better than the Tigrinya or Amharic or whatever of the interviewer.
Even if the interviewer studies the language for a few months they still won't be good enough to conduct a decent interview. When I learnt Spanish after about 12 weeks we had to do a one or two minute presentation on a subject of our choice at the end of the class. You'd be shocked at how much people struggled and that's speaking for a minute with unlimited time for preparation, memorising, nothing to respond to, no questions.
You want him to study Tigrinya but what about Amharic, all of the other languages. Also look at their alphabet:
It looks difficult.
For him or anyone to get up to interview level is going to take a lot. I don't think people realise just how good the English is of most of these athletes to be able to say what they say/respond etc.