i thing best practice is PHx:
1. make snippet with name phx:date_lang:
<?php
/*
* description: output date with language settings
* example: [+string:date_lang=`format`+]
*/
$format = (strlen ( $options ) > 0) ? $options : '%a, %d %B %Y';
setlocale ( LC_TIME, 'bg_BG.UTF-8' );
$date_bg = strftime ( $format, 0 + $output );
return $date_lang;
?>
this line is your line:
setlocale ( LC_TIME, 'bg_BG.UTF-8' );
put your language and everything is fine.
How use? For example:
[+comment.createdon:date_lang=`%a, %d %B %Y`+]