first sorry for my bad english
Some users would be able to personalize the language-package. It is very uneasy after an upgrade to merge the own changes with all of the language-files.
I have a suggestion:
Put into any language-files at the end the follow lines
//--------------------------------------------
if(file_exists(__FILE__ . '.user')){
include(__FILE__ . '.user');
}//--------------------------------------------
and any user will be able to use own personalized language-files with the extension ".user". If there is a new upgrade the user only have to put the *.user-files in the lang-folder and thats all.