Macedonian language
One such feature is the replacement of the hard sign, such as: Ъ > о, Ь > е (сон, темно). This change occurred in the 10th century and is quite represented in Old Slavic texts of Macedonian origin. Unlike Macedonian, in Serbian and Croatian these vowels merged into one sound - a (сан, дан), while in Bulgarian they merged into Ъ with the difference that before Ь the soft pronunciation of the consonant (сън, дън) was kept.