> many places declare only one of the variants to be legally binding and the others only for convenience
Variants of what?
Translations. Say, the English one is the official and legally binding one, and the Chinese and Spanish translations are only for added convenience, without any legal effect.
Ah, got it. You typically have to say that really explicitly in all the languages. Also, it depends. Generally speaking, best practice is to have one and only copy and then a phone call where it's explained however. Better practice is not to take legal advice from my Internet comments, because I am not a lawyer :D.