I've been playing the electronic piano almost every day for some time now. I do it at a very primitive level because I started late and have little natural talent for it. But it's fun nevertheless.
Just like weekend golfers sometimes watch the majors on TV, I sometimes listen to famous pianists on YouTube. Would I be able to tell them apart if there was no video? No. They all sound equally great to me. Very rarely I think "he's going too fast" or "too slowly". Nothing more complicated than that criticism-wise.
As everyone knows, YouTube always flanks the video you're watching with a column of related videos. If you're listening to a piano performance, some of the related videos will show other pianists playing the same piece, some will show the same pianist playing different pieces and some will show the pianist talking about his work or whatever. I've got low attention span, so I click related videos all the time.
A while ago I noticed something. Daniel Barenboim, one of the most famous piano players and conductors of our time, speaks a surprisingly large number of languages. Here he is giving an interview in German. Here he is speaking French, Italian, English and his native Spanish. And here he is giving a speech in Hebrew. I remember someone saying, in a YouTube comment I think, that he once heard Barenboim talk to his half-Russian kids in Russian at an outdoor cafe. Unfortunately I did not find any videos of the maestro speaking Russian on YouTube.
Maybe I'm wrong, but I've always assumed that top-level piano playing works a lot like golf, tennis, chess or ballet. Meaning that success in it requires two things: a very high level of natural talent and an enormous amount of practice. Having just one of those things will make you a mediocrity in the field because there will always be some people with both talent and work ethic. And they will overtake you if you're missing either one of them.
Since millions of kids start playing the piano every year, the best players of their generation presumably have levels of natural talent and hours of practice that are very close the maximum attainable by humans. And, if sports is any guide, the performance level at the very top would be similar. Even at their peaks Federer and Tiger Woods routinely lost big tournaments to rivals.
So how could Barenboim have had time to learn five foreign languages? I see two possibilities:
1) Perhaps the maximum amount of piano practice one can do in a day is not the same thing as the maximum amount of practice in general that one can do in the same period. I doubt that over long stretches of time anyone practices any musical instrument (or any sport) more than, say, six hours a day. Why do people stop? Mental fatigue. There is a maximum level of monotony that each person can take. Obviously it's lower for lazy people than for hard-working ones, but everyone has a limit.
Perhaps after maxing out one's ability to continue practicing the piano one can practice something else. Would it break the monotony just as well as vegetating in front of the TV? Probably not, but it could still break it. And maybe that's what Barenboim did. By the way, his English, German, French and Italian (I can't judge Hebrew) are accented, though very fluent. That means that he must have mostly learned them after the age of 13. Which is more difficult than learning languages in childhood.
2) High-level language study (and fluency in 5 foreign languages is very high-level) can be fundamentally different from high-level music learning. You can't get good at the piano without effort. I think it IS possible to learn languages without much effort, just by talking to people. I'm a big nerd, so I mostly learn languages by reading. That does take effort. But a naturally-talkative person could probably learn them without it feeling like practice at all.
If I had to guess, I would pick a combination of 1) and 2) in Barenboim's case.