In my research job, one of the reasons we sometimes use focus groups is that they enable us to include a larger number of non-English speakers (or limited English speakers) in the study. This is useful in cities such as NYC or London, where there's a lot of diversity. In many cases, the focus group members have helped each other with translating, or clarifying what they want to say. (It's also far less costly than hiring a translator for individual interviews.)
I'm sure you're well aware of some of the challenges involved in moderating focus groups, but this is one example of how it can make your data pool more inclusive.
It sounds like an interesting research project!