In my experience, bilingual sites are usually one of the following:
A - officially bilingual with matching language equivalence, everything in one language appears in the other. Our Canadian Gov. sites are examples of this.
B - Bilinqual with content matching unique needs of each language group. Site structure is the same, but items only translated when strongly relevant to the other language group.
C - Bilingual in interface, and mixed in content. These sites permit the user to select the language of the interface. The content, usually DB driven, is served up in the language entered. Sometimes users have the option of seeing results in one selected language.
The strategy and approach for each is different. DB design and content management techniques also differ.
You can see our recent work on an example of B and C above at:
http://www.prevenstroke.ca/ and
http://www.preventstroke.ca/public/francais/program/ProgramSearchFr.aspx
ASM
http://www.itscooperative.com/community/