Sometimes after webserver migration you can loose some configuration especially in regards to language conventions.
In this case I will describe how to solve the missing language issue in PHP and setlocale().
The answer is pretty simple and you can find it here if you use a Debian like system.
Access your shell and edit the following file decommenting the language you want to enable
After saving the file run:
and the issue is solved.
Remember to restart Apache, NGINX or PHP-FPM based on your webserver configuration.