Users choose which language of dashboard

I am doing a project with speakers of different languages. We are using a wordpress site like a wiki to gather our work. I would like each user to be an admin and to see the interface in their preferred language. We will work in French but I want the interface in English, some in French, and still others in Spanish. I can’t for the life of me figure out how to do this.

I created a new user but don’t see a way to say which language to make the interface in. I created the site and so it is in English but others will not be so comfortable in English. I would love a solution that does not involve a plug in but I’ll go that route if I have to.