With no copyright info this is almost certainly a bootleg deck. It’d be interesting to see all 6 sizes of the deck box to verify. It looks really cool though!
I may live in Japan, but I don’t consider myself an expert still. That being said, the front cover definitely looks like Chinese instead of Japanese. Most Japanese has at least a little bit of hiragana or katakana somewhere within a sentence or phrase. And Pokémon products often don’t utilize full blown kanji due to the fact that children often can’t read many of them yet.
I can read both Chinese and Japanese.
(Chinese at an intermediate level, and Japanese at fluent level)
I can whole heartedly say that the primary displayed language is Chinese.