Interestingly indeed, since the first thing that occurred to me was: oh, I didn't know Fischer spoke Serbian. Then, some time later, it also occurred to me: hang on, I thought Fischer knew Russian. Presumably I was uninformed on the first point and wrong on the second - or at least, if he had some knowledge of Russian it was not enough to hold a conversation in that language. (Of course there are all kinds of levels of foreign-language comprehension and it wouldn't be unusual for somebody to be able to read a language to a reasonable standard but have much less ability to speak it or to understand it spoken.)(Interestingly, we communicated in the Serbian language, the only one that was known to us both.)
So I wonder - what knowledge did Fischer have of Russian? Was his Serbian fluent and when did he learn it? How good was his Spanish? (The clip is not really long enough for me to judge: I am sure there is an anecdote somewhere about him translating from a radio broadcast, but I can't quite place iot right now.) Do we have any concrete evidence that he had other languages beyond these?