New translation interface
The new interface was tested with many diverse users, who found it intuitive and nice and said that it makes their translation work more efficient. They reported some issues, which were fixed. So the developers have a good reason to believe that the new interface is better than the old one.
If you have particular comments that can say what exactly is wrong with the new interface, the developers can do something about it. Comments like "disgusting" and "messy" are not helpful.
"the developers have a good reason to believe that the new interface is better than the old one." The developers? I really, really don't understand what you are doing (with "you" meaning the WMF). Did you ever considered to ask the community? What they want and need? The community does not care what the developers think. Developers always tend to reinvent the wheel no matter if the old wheel was good enough for everybody that used the wheel (I know this, I'm a developer too). What was the problem with the old interface? Currently the new interface is a total mess. In all browsers. (I tested it with IE 9, Firefox 9 and Opera 12.) Nothing is better in the new interface. Features are removed. Buttons do not work or are misplaced. It wastes insanely huge amounts of space while at the same time important information are hidden in tiny little iframe popups that can't be enlarged. This does not make any sense.
At least keep the old interface. You can't kick the community in the face and force them to switch to a worse tool without asking them. You (the WMF) did this so many times. Didn't you learned something? LiquidThreads? Gone to hell (not here, obviously, but everywhere else). The Article Feedback Tool? The users said "burn it with fire". To bad the translatewiki community is a minority. You will not hear much protest. This does not mean the new stuff is better. It simply means the users stopped to care years ago. And so will I if you ever delete the old, very well working tool. I will not use the new crap. Not as it is.