This page has a comprehensive list of dojos in Zürich and elsewhere in Switzerland: http://www.aikido.ch/state.asp?s=6
I have not been to any of them yet - I was training in Basel before.
Of course it depends on what you class as traditional Aikido - the Swiss Aikikai style seems to be quite flowing and I find it close to what I did with the Aikido Fellowship in the UK. The UK Aikikai style I always found a little on the abrupt side.
As for the English only part, I would not worry too much as very often instructors will speak a bit of English if your really don't understand. To be honest I found it a convenient way to improve my German comprehension.