"Excuse me, where is the men's room?"
Translation:Извините, где мужской туалет?
"Men's room" in English implies the men's bathroom, not just a room for men or what have you, while in Russian "мужская комната" does not have such an implication, and just refers to a manly or masculine room.
So if I'm talking about a room for men in a hostel or something like that I have to say "room for men" not "men's room"?
In the UK, you'd be OK saying: "the men's room", because it does NOT mean: "the toilet". If you wanted the men's toilet, you'd ask for it. We're not squeamish about saying the T-word, so our way is more like the Russian way. A "men's room" would be a room that is in some way dedicated to or reserved for men - so possibly a dorm in a hostel or something, yes. Equally, we don't use "restroom" to mean: "toilet", and when we talk about "the bathroom", we mean a room that has a bath. A bathroom may or may not also have a toilet - usually does. A room that has shower only may be "the shower room", or just: "the shower", but if it has, say, a toilet and a handbasin as well, it probably goes back to being a bathroom, even though there isn't any bath in there! Confused yet? ;)
Well, if you just asked where the men's room was, you'd almost certainly be directed to the men's bathroom. "Men's dorm [room]" or "men's bunk [room]" could be used to distinguish the actual sleeping quarters. Hostels are relatively uncommon in the US, and virtually unheard of outside major cities (I've never stayed in one), so ad hoc terms would likely be used.