I only know for sure that as database they use MySQL since it is fast. But according to some sources they use many different server technologies: Java, Python, PHP, Ajax and other server technologies.
If you are applying for a job at Google, you will probably need to know Python because Google depends on Python a lot. Also, Google's appspot uses Java to work.
Have you tried to ask "which technology yahoo uses" "which technology windows uses" ? I am sure you didn't find a definite answer. In my opinion, they use a large "cocoon" of interconnected languages,system etc.. and this forum is not even enough to elaborate it. Try to ask more specific questions next time. "Technology" and "google" keyword is as broad as the distance of Earth to Jupiter. LOLS