You should be able to wake up hungover anywhere where that language is spoken and get around, no matter which problem comes up. That's my definition, at least.


Since work sometimes includes even more specific vocab, that's kinda hard to answer, because people could just study those words and maybe not be all that great in the rest of the language. They'd still need a decent grammar, though. It probably depends on what work you do. As soon as your partner switches to casual conversation and you're lost it would probably be better if the never assumed you knew it.


I can only answer that from my POV: I thought about adding Swedish, just for the heck of it, because I understand some and can speak and construct a few sentences that would help me survive if I was stuck there. I only picked up this knowledge during my various visits, though, so it's very basic.
But I wouldn't add French, because I forgot almost all of it even though I studied it for 5 years. I still can decipher some things in written form but unable to construct my own sentences, so it's not worth much.


Considering all of the above, I can honestly only list German and English.