Go to
www.zumba.com and search for the city you want to take classes in. There will be a list with the instructors details so you can contact them in advance.
I only speak english and have been doing Zumba with a non english instructor with no problems. They actually hardly speak during the class - which is standard for Zumba classes - they almost 'mime' the instructions for lack of a better word - and you just follow along.
You may also be able to watch or do a demo class before signing up to anything long term.