Nonik, you show good example…
In Serbian, there are two linguistic standards in replacing old yat letter, Ijekavian(Montenegro and BiH) and evavian(Serbia and Macedonia), like in words: Mleko(milk)-mlijeko, vetar(wind)-vjetar, cvece(flowers)-cvijece… In ijekavian dialect, it depends how long vowel is, if it is long accent, like in word "mleko", than it's mlijeko, if it is short, like in word vetar, it's vjetar.