I see some debate about "untranslateable".  Ultimately I imagine almost anything is explainable, but some things may verge on  - or actually be - untranslateable.

Surely there is a spectrum - from a word in L2 which exactly fits in every way, or which doesn't fit that well for a variety of reasons, to a phrase, needing a footnote, or telling the reader to go off and read an anthropology tome they don't have.  I have read explanations of Shakespearian and ancient Greek jokes where it has taken me several decades to start laughing.

  How does one translate the French tutoyer into English?  Speak informally, or what? It might be an insult or it might be a compliment, depending ... 

And I remember speaking with an African translator who told us his nomadic language lacked a word for harvest - and there were people who had never seen (or imagined) such a thing.