What do they call weed in japan?

The Japanese native Word for pot is 大麻　（たいま）　which is pronounced "taima."

"tai" rhymes with the English "tie", "ma" sounds like "ma" in the German "Mann".

The kanji means "big" and "hemp", respectively.

Oddly enough, most Japanese don't make the correlation between hemp and cannabis, though hemp has been an important part of Shinto for a while.

Another Word used in Japanese for pot is マリファナ　pronounced "marifana".

It was adopted from the English Word, as were many other modern Japanese Words such as "レスタラン"　("resutaran", or restaurant) and アルバイト　("arubaito", or part time job, from German "Arbeit").