On Linux, setlocale() depends on the installed locales. To see which locales are available to PHP, run this from the terminal:
"locale -a"
Provided list are all locales that are available on your server for PHP to use. To add a new one, run
locale-gen <locale name> (this may need sudo / root permissions), for example to add a Czech locale, run something like this:
"sudo locale-gen cs_CZ.utf8"
Then you can use this locale declaration:
setlocale(LC_ALL, 'cs_CZ.utf8');