Language problem in Production [solved]

You can check with the debug toolbar if your language files are loaded or not. Also make sure to name your file correctly: first letter is uppercase and the rest is lowercase. Like this app/Language/en/Validation.php If your test server is on Windows it will probably work even if it's not correct. But the file systems on Linux is case sensitive. So it's important to name the files correctly.

Thanks, man! This one worked like a charm! I didn't even think about it. My language files were 'app.php', now they are 'App.php'.
But strange that unix on my MacOS X worked with the files 'app.php'.