[FLOW3-general] Labels translations based on user's language

[Sergio]

Hi list,

I have a "User" class that extends "Person" class (Party extension) and
I've added "language" field as the user's prefered language for the website.

I've read this guide about internationalization:
http://flow.typo3.org/documentation/guide/partiii/internationalization.html

And I understand XLIFF formats and I've got all my labels ready to
translate, but how do I do the website detects this user's language?

Any hints would be welcome.

Thanks in advance,
Sergio