[Dev] Clear explanation on why LANG matters to Apps?

[bp]

Excuse my ignorance, but when I install some J2EE/WebSphere app on a 
Linux machine setup in Spanish (or any other non-english language) what 
really causes it not to work?  Are apps typically written for English 
because of the path differences on a Spanish install?  Is Java unable to 
parse properties files in Spanish...? 

Just looking for a concise technical idea of what makes an app language 
dependent.  My first assumption would be that it *should* work but 
acknowledge that any output would be spit out in English...  but it 
seems Java takes exception (pun intended) to it's non-English appserver.

-bp