While trying to install Owncloud I encountered the following error:
Setting locale to en_US.UTF-8/fr_FR.UTF-8/es_ES.UTF-8/de_DE.UTF-8/ru_RU.UTF-8/pt_BR.UTF-8/it_IT.UTF-8/ja_JP.UTF-8/zh_CN.UTF-8 failed
Please install one of theses locales on your system and restart your webserver.
For Debian Linux the solution is very simple, just run the following command:
And mark at least one of the locales you need.