One school I went to is Dance to Dance in Marktplatz, Basel (www.dancetodance.ch)- the classes are in Swiss German initially but most teachers are able to translate if necessary. Also, if you sign up without a partner they will try and find one for you - often someone who is more advanced but willing to dance with the 'newbies' - a great way to learn! They do a wide variety of dance classes and as a not-very-good-German-speaker I would recommend them. It's also easy to follow the visual clues!