The problem occured if you are using non-latin language for your shop and default browser codepage is non-latin too.
To solve the problem it is quite enough to add just one code line into index.php and admin/index.php files.
Below is the code (added lines are bolded):
// Output
$response->setHeader('Content-Type', 'text/html; charset=utf-8'); //added by vot
$response->output();