This makes me wonder, does Japanese have an equivalent to the Chinese concept of a chengyu?
Besides that, there is 慣用句 kanyouku, which means just an idiom in general, and isn't restricted to kanji expressions. And 決まり文句 kimarimonku, which means something like a "cliche phrase".
Sometimes you will have to map between simplified Chinese characters and modern Japanese characters. Easy enough though, since they still look very similar.