Translation:My son is at his best friend's house.
I think what we're seeing here is that chez is not literally "house" but more of a fuzzy concept about "home", without necessarily being translated as "home", "family" without necessarily being translated as "family", or somebody's "place" without ever translating it as "place", e.g., acheter quelque chose chez l'épicier = to buy something at the grocer's. Chez is a French word that does not have an equivalent in English so we struggle with it and feel like we just have to put something in there. But the answer is, no, we don't. http://www.larousse.com/en/dictionaries/french-english/chez/15106
Yes. It's very common here in Britain. "He is very pally with my boss." Most people in my part of England use matey in the piratey sense (although without the accent lol). "Hello there matey!" A sort of casual affectation when bumping into a dear friend. "Mate," is far more common though... and slightly more serious... although still very casual. Goodness, even the casual everyday language we take for granted has layers of complexity.
"meilleur" is an adjective:
- bon, bonne, bons, bonnes = good
- meilleur, meilleure, meilleurs, meilleures = better
- le meilleur, la meilleure, les meilleurs, les meilleures = the best
- son meilleur, sa meilleure, ses meilleurs, ses meilleures = his/her best
"mieux" is an adverb:
- bien = well/good
- mieux = better
- le mieux = the best