I want to buy IDN domain but I am not sure how is's going to look in a browser. Like, will users see xn- part or it will look just as normal in my language ?
Here is a handy explanation for you on how it works: https://www.name.com/idn
Essentially any non-local user whose system doesn't support your language will see xn- url, but any user whose system has that language installed will see appropriately converted url.