"They do serve Vietnamese here (try their Pho bo), but also mostly Thai-style curries (from hot to mild, with and without meat, or with fish).
Also good is their Tom Yam soup.
The place is quite small and packed during lunch, because it's not expensive.
I eat there very often (it's next to our office) and I still like it there ;-)
I don't know about the English service, but they do speak French there (and there are most times other guests you can just ask).
Also see the reviews here:
http://www.zueritipp.ch/dyn/gastro/index.html?lid=8360"