I have not been able to install 6.0 yet but I would try Webupdater in your case. Might also be possible to reinstall language files with GE, but I am not sure.
With Garmin Express (windows v5.6.2.0), I saw 23 updates available including the software version 6, language files, sensor hub, ... I clicked on install for the software version, my watch is updated but I lose the other update available. In Garmin Express, I didn't have the possibility anymore to install other languages (as it was the case with previews version). (And I don't know if the sensor hub was updated) I installed other language via the WebUpdater application (only possibility found)
my workaround 1. reinstall language by webupdater (german available on watch but take no effekt) 2. reset my 935 to default and now german available, selectable and funktional
is there a way to add additional language pack? e.g. Chinese or Japanese. found this link below: http://www8.garmin.com/support/download_details.jsp?id=11785 but it seems it has to work with GE. the problem is that I could not see Chinese or Japanese file in GE