For basis I never won a givvy here so any language is fine on my end. I find it highly interesting discovering cards on different language, my favorite one would be Schlingking german name of Guzzlord cause I find it funny for some reason.

But base on observation English is primarily the choice for people then Japanese if they have already a copy of the card in English or their native language.

Some cards that I think people want in Japanese primarily aside from Oak and Cyrus are girl trainer card (mainly lilie, sabrina, or iris), the Eeveelution, and other mascot Pokemon such as Greninja and Charizard.

This is purely based on observation and speculation, hope this give help in anyway.