If I spoke Russian and was POTUS I certainly wouldn't let a major Russian journalist interview me without a translator that I trusted. I may understand everything they say but I could miss some local word, slang or dialect - or some subtlety that could embarrass me, the US, or Russia. It would be much safer with a translator.

Now if I were POTUS and I was walking with Putin alone, a translator would be unnecessary. Both of us would understand one or the other may get a word wrong and it would be between us - not in front of the world.