I'm French and I see this all the time, even Outlook, given the right conditions, will gives you this in the default folders, Inbox in French is "Boite de réception".
If you happen to be using Windows configured in a foreign language the first time you start Outlook, your inbox, sent mail, etc, folders are named according to that language, and will never change, and you'll have to live with non-standard names for the folders.
At least its teaches you how to configure folders manually in most email clients.
For anyone who doesn't know OSX, this translation happens on the UI level. Typing ls in a terminal gives you the real directory name.