Structuring site with multiple subsites
As of this comment, Craft 3 is still in beta but you may want to consider it as your challenge sounds like the new Sites functionality may be a good fit.

Sites, allow you to manage multiple websites and multiple languages in one Craft installation. You can find a longer discussion and some examples here: 
Managing Multiple Sites in Craft 3 – Sites and Localization

You could create a Site for each combo of Garage and Language that you need to manage. For example:


Garage 1 - French
Garage 1 - German
Garage 2 - French
Garage 2 - German


The blog and other sections for each of these sites could be managed under one channel. Admin users would be able to switch between each subsite just as they switch between locales when editing an entry. User Groups could be created for each subsite as well as the permissions in Craft 3 will allow you to restrict a users access to a specific subsite.

You can read more about how to configure each site in this Localization Guide in the Craft docs. You'll need to configure a couple of files for each site and make sure your DNS is pointing to the right place for each subdomain. But once you get those items setup, you should be able to use the same templates for all of the different sites and languages.