Japanese cards vs English market value

How are you determining market value for Japanese cards. I had someone approach me recently about buying two cards off me. The English versions of the cards are around $125ish combined. TCGplayer and sites like that seem to only be English. Is there a rule of thumb for this? Is it a certain percentage of the English cards? I looked on eBay but the prices are all over the place so it’s hard to get an accurate read.