Check out the LocaleSwitcher module in the app store. If the UI doesn’t give you exactly what you need, you should be able to modify it to meet your needs. It handles the tricky part of changing languages and reloading the user’s page.
There are a few solutions scattered around the forums: See https://forum.mendix.com/link/questions/91821 for the most recent one as well as a few ideas raised in the corresponding forum: https://forum.mendix.com/link/ideas/1196 and https://forum.mendix.com/link/ideas/441
Hope this helps.