What should I say to propose marriage to a Japanese women?
You can say
「私と結婚してくれませんか?」 僕と and 俺とare good, too.
also :
結婚してください!
結婚しませんか?
結婚しましょうか?
Usually say "marry me"(kekkon shite kudasai結婚してください). It's a direct way of speaking, but there are many other ways.
How about in Belgium?
in French: Veux-tu m'epouser? Or even: Veux-tu me faire l'honneur de m'epouser?