A packaging mistake led to Ardour 3.1 being released without any translation enabled. Ardour 3.1.10 is now available for those who prefer to work in one of the translated languages (German, French, Spanish, Portugese, Norwegian, Italian, Russian and others).
There are no other functional changes compared to 3.1. The source code release remains unchanged (since translations are generated during the build process).
You can get it as usual from the download page