Language of days on calendar

Hi! I need specific changes for my site http://www.nov-sh.com/?cat=4 As you see on this page I use widget calendar and it show me days in English format (M T W T F S S), I need change it to (П В С Ч П С Н), becouse my site on Ukrainian language. I see via inspector (F12 in mozila) that code look like <th scope="col" title="понеділок">M</th> <th scope="col" title="вівторок">T</th> and the same lines. Can you tell me where I can change this letters to Ukrainian or how can I change date format or else to see Ukrainian letters in calendar. Thank You!