RU: Kogda wy rodilis'? Or, Kogda ty rodilsja?
The palatalized "s'" at the end of "rodili" and the "sja" at the end of "rodil" is the direct Russian equivalent to the Polish się.
Out of curiosity, how would you say "when is your birthday?" (if you think about it, they mean literally the same in english)?
Kiedy są twoje urodziny? / Kiedy masz urodziny? (When do you have birthday)
Well, not literally the same, you won't get the year of birth after you ask "When is your birthday"...
In Russian, we have dień rożdienija, and in Ukrainian deń narodżenia. Is there a comparable phrase in Polish like dzień urodzin or something like that?
'dzień urodzin' is more or less like urodziny itself. For example a birthday card may start with the words "W dniu urodzin". But 'urodziny' are just easier to use.
'narodziny' is the moment of being born, and that's where "Boże Narodzenie" (Рождество) comes from. But the "birth date" will be "data urodzenia".
It's also interesting that "births" are plural in Polish when referring to one person