With Language Settings for Groups, group creators and admins can choose the language for particular groups on the "Edit Group" page, and all parts of the group's interface will appear in that language. When participating in a group with its language set to French, for example, phrases like "Started by" or action links like "Favorite" will be translated to "Créé par" and "Favori." Even better: All email notifications received from participating in the group will be in French, too.
Members already post in French, (or any other language) but they previously were forced to use an English interface. With this new option, they'll have a much more native and comfortable experience within the group.
Member-generated content won't change, remaining in whatever language it was posted in.