In German we call it “tailor’s seat” (Schneidersitz).

Boring fact: it’s also “sit like a Turk” or “sit the Turkish way” in Russian (сидеть по-турецки).

Now I’m curious what they say in Turkish.

UPD: me and @TheGreenGolem@lemm.ee are referring to the Lotus position which is what it is called in Turkish.