Knowing a good bit of French when having car trouble in very rural Quebec proved very useful for us. The locals were not very English-speaking. Also, the language that we are learning is spoken in the place to which we plan on traveling so I expect familiarity with it might be somewhat useful, But perhaps that's just me.
To each his own, if people choose to spend time in a casino gambling against a house with odds favoring that side of the table, so be it. I prefer doing things much more of personal interest and learning/seeing something new. Of course, the difference between us is vast in terms of respective interests and outlook upon knowledge.