They don't have to get all countries on the same page; for example, they could default to only allowing apps to be sold in the country of the vendor, then expand from that to countries with an extradition treaty with the vendor's country.

Also probably not quite as hard as you make out in practice, as 27 of those countries share membership of a super-national government whose specific purpose is to make trade easier by streamlining legislative differences between them, and that block plus two other single countries constitute about 60% of the world's GDP.

Though random small-time scammers may regardless have a hard time selling in China an app made outside, and vice-versa, as even just the language barrier can be quite intense — I've played a game where the decently resourced western publisher didn't notice (or noticed but didn't fix) the fact that the "choose your name" box only had room for one character, and thus I was the only player who had an interesting name like '狐' rather than 'M'.