Is there a word for "kosher"? I'm looking for a translation of the word kosher in it's most strict sense: a food that is apt according to the jewish law.

Google translates kosher as 犹太, but if I'm not mistaken, that just means "jewish". And you can certainly make non-kosher jewish food.
Depending on the context, there are different strategies for translating this word. In the most strict sense, leaving nothing unsaid, it is （符）合犹太教规的 when it comes to food preparation. If reference to 犹太教 isn't essential to the context, it can simply be 合礼法的, because the notion of doing things according to 礼法 is prevalent in Chinese culture.