In my experience, there are a lot of people selling foriegn cards that dont know there Pokemon card values. I dont claim to be an expert on prices, but I can tell you that a Hidden Legends rare should not cost 10 dollars in any languages. Yet you often find low value English or Japanese cards to be expensive in any other language. The price of the cards should be close to the English counterpart fo at least the European languages.
I'd say exceptions would be Korean and Chinese Base, Korean 4rth gen, Unlimited Jungle and Fossil Dutch as well as 1st ed Base, Any RH, Holo, or UR from 3rd gen Portuguese sets and maybe some of the 4th gen UR's for 4th gen Spanish. Almost everything else shouldn't be insanely expensive as they often are. Thats just my opinion though. Cant really speak for Japanese though as the market for those can really change things.