Yokohammer wrote:"Waste not want not" is probably the closest standard English equivalent to "mottainai." Sort of an English "四字熟語", even.
There's usually an English equivalent (or two or three) to any of of those "this Japanese is unique" things, but people just don't want to know. Even commonly cited examples like "gochisou sama deshita" (I mean what the heck is wrong with "thank you for a delicious meal", or just plain old "thank you" which, in context, means exactly the same thing), and "gokurou sama," etc, etc.
So, how would you translate "gokurou sama" in naturally sounding English? Something like "You must be tired, take it easy"?
Edit: Now realizing that that may be a more appropriate translation for "otsukare sama".
I guess "gokurou sama" would be something like "thanks for your efforts", or "thanks for your hard work"?