For a while now, when I go into Magix support, in English, as soon as I click on Customer area the interface changes to French. If I go to the bottom of the screen, select the map and change to English, it comes back to the first area that is shown after logging in. Press on Customer area and it's back in French. Is this just me or can someone confirm this.
I am getting the support area in German at the moment, however this is because I am in Austria at the moment - changing the language behaves as you have seen.
I suspect the geo-location feature of the website sees your Province as French and that is causing the issue with the language override in the URL not working as above.