[XeTeX] Multiple citation styles in a single document

[Pierre Morel]

Since the "biblio" mailing list seems to be rather inactive, I'm posting on this list to which I'm subscribed, sorry for my question being not directly xetex related (even if I'm using xetex!).

I'm writing my thesis in French, but it includes my published or to-be published articles in English. All is in a single document in order to have correct figure and page numberings (but with multiple .tex files of course). I use natbib for the bilbiography.

After my problems with hyperref, which were quite minor and are solved, I'm stumbling on something much more serious:
Depeding on the bibliography style I choose (plainnat or plainnat-fr), the language in the citation changes, the most obvious one being the switch from (Author1 and Author2, year) to (Author1 et Author2). The first being quite unsettling in the middle of the french parts (because of the "and") while the second looks weird in the english parts. For more than two authors, the typography changes on the "et al" (normal text for English, italic for French).
So my question is the following : how to choose two different citation styles for different sections of the same document ?
(only the first \bibliographystyle{} command seems to be taken in account).

Thanks,

Pierre