Info about XSLT with Java servlets

Hello everyone

I hope someone can guide me a bit on this.
I am working on a project where there is a problem with the language.
Basically, if I set the language of the form to one language, everything will be translated to that language and also the details inside the drowpdownlist etc.
If I go back and choose another language, the label stay the same but information inside the drowdown box change back to the first language that was chosen; so at this point no matter what language you choose, the information will be of the first language that was chosen.

After debugging I narrowed down the cause of the problem and to me it seems like it has to do with HTTPSession; this is because if I clear cookies and everything and then choose a different language then everything works but when I choose another language(withouth cleaning anything) the first language seems to be set by the system.

I wanted to ask whether you can tell me how I can spot the problem and debug it effectively as I never done debuggin in a web environment where different technologies are used such as xslt,javascript and java.

How can I find out what file the form is actually calling and then from there see what's going on?
and
What do you guys think could be the problem in this case, why the HTTPSession is not replacing the value of the attribute when the language is changed?

Thank you

P.S: I am using Eclipse and tomcat