locale.php trouble

I changed the names of days and months from in English to Bulgaria in locale.php but two problems appeared
first in the calendar the sort name of a month is diplsayed only with the foirst caracter followed by ? – eg – Ñ?? instaead of Ñ?Ã?½Ñƒ
and second on the login page I got the following error message:

Warning: Cannot modify header information – headers already sent by (output started at /home/dodica/public_html/test/wp-includes/locale.php:1) in /home/dodica/public_html/test/wp-login.php on line 42

Warning: Cannot modify header information – headers already sent by (output started at /home/dodica/public_html/test/wp-includes/locale.php:1) in /home/dodica/public_html/test/wp-login.php on line 43

Warning: Cannot modify header information – headers already sent by (output started at /home/dodica/public_html/test/wp-includes/locale.php:1) in /home/dodica/public_html/test/wp-login.php on line 44

Warning: Cannot modify header information – headers already sent by (output started at /home/dodica/public_html/test/wp-includes/locale.php:1) in /home/dodica/public_html/test/wp-login.php on line 45
WordPress

any ideas?