To install nightlies, go to your settings (cog icon in the upper-right corner) select Nightlies as your preferred stability, save, go to the explore tab, and either install FSO from there (if you don't see an install button, go to the details page). After that you should be able to select the nightly build you just installed on the dev tab on the "FSO Settings" tab or by opening a mod's "FSO Settings" window from the context menu on the Home tab.
With a bit of additional work we could probably localize Knossos but I currently lack the time necessary for this. You'd need someone with Python and JavaScript experience for this.