What's the main language there

Zurich is in the German-speaking part of Switzerland, and while those who dislike German as a language opt for a French course, it won't be much use to you if you live and work in Zurich.

There are a variety of language schools in the Zurich area, so finding one that fits your needs shouldn't be a problem; but keep in mind that even after learning some German, you might not always be able to follow conversations between locals at first, 'cause Swiss-German takes some getting used to

But learning High German will already give you a an advantage both in the work place and everyday life.

best of luck!

I live in Geneva. Here French is spoken.

If you work for a bigger and international company English might just be enough. However, for daily life in the Zurich area learning German should be your choice. Although, like HipMom said, locals use Swiss German for daily life all of them understand and speak High German as well (if they want to... )

For a first impression of Swiss German check out the Swiss German dictionary Swiss German dictionaryI have on my blog.

For language schools I recommend Migros Klubschule but there are other good schools in the Zurich area as well.

There's 3 Speaking in Switzerland... Italian, German, and French...

There are four national languages of Switzerland:

German, French, Italian, and Romansh.

See:  http://en.wikipedia.org/wiki/Romansh_language

They speak Swiss German on Zurich. It's a bit different than "German German", they say, so you should take Swiss German classes!

If youre staying in Zurich you should definately learn german

If you are able to pick up languages quickly, learn both Swiss German and High German, in that order.

Speaking English will probably be enough if you are working for an international company in Zurich, and learning Swiss German will be a big help for your regular life in Zurich. If you are adept at picking up languages you should then add High German as it will be very helpful if the company you work for deals with other companies in Germany, as Germans cannot really understand spoken Swiss German!

There are some big differences between Schweizerdeutsch and Schriftdeutsch.  If you speak Deutsch then you should have little trouble with Schriftdeutsch but Schweizerdeutsch may be alien to you.  Schweizerdeutsch is the language of Zürich but everybody learns Schriftdeutsch in school.