日本は 世界遺産の数で 世界12位ですって英語でなんて言うの？

"Japan is 12th on the list of world heritage sites. " This explains that on the list of heritage sites in the world Japan is listed at number 12. "Japan ranks 12th on the list of world heritage sites." This is another way of explaining that Japan is 12th on the list. EG: Where does Japan rank on the world heritage list? - Japan ranks 12th on the list of world heritage sites.

within the rankings, describing in the ranks (top 10 or 20 ect). these are casual and easy ways of describing the rankings/positions made by the World Heritage site.

If something is ranked then it is placed in a certain order depending on criteria so you would say 'Japan ranks 12th in the number of World Heritage sites' this means they are 12th on the list or the 12th from the top

If you rank something, you place it in order according to certain criteria.

All these statements view the ranking in a honourable and positive way to whomever you are speaking. The first statement is talking to someone within your country so naturally they know that you are speaking of Japan.

This is the type of phrase that a tour guide would share with people on a tour. Because of this, I am using some more formalized language like someone would use in a presentation. The phrase "In terms of" is often used to clarify by what measure something is being examined. In this case, we are using world heritage sites.