Problem by deploy with the language

Hi!
I have just developed an application and used the package tool to deploy it by the customer. When I extract the package, seems all to be installed correctly. When I run it there are a couple of runtime errors that doesn´t happen if I do it but what is more strange, I have developed the application with two languages (german, as default language, and english). The client computer is set to german and I got the labels in english. Apart from
the local settings, is there a possibility somewhere else to affect the language that should be shown? Can it be a problem from the configuration of the machine (maybe service pack)?
Thanks in advance.
Jaime