alt Hacker NewsGood question. I chose them because they are the languages that I use professionally and would choose for technical interviews. I expect to be asked to solve problems in either language in any given interview.
Technical interviews are different enough from day-to-day work that I still find it valuable to practice in them.
I hope you really do it more as enjoyment (like people do crosswords) with just a very secondary benefit of technical interviews, because otherwise I can't but find this rat race obsession super sad.