"Nem kint írunk, hanem bent."

Translation: We are not writing outside, but inside.

[SedatKlc]

why don't we say írünk and írek for I, is it irregular?

[jsiehler]

The vowels i and í are neutral as far as vowel harmony; they may occur in either front- or back-vowel words. When you have a word like ír or ing or híd or víz in which i/í is the only vowel, you can't determine the vowel harmony just by looking at it - you have to memorize it.