I BRING YOU NEWS:
The Wikiers have finally found transcriptions of the lyrics to the new songs. Proper translation is apparently ongoing, so we should be seeing something soon!
In the meantime, we now have a plot description for The Long Wall and the Watchman: Basically, Elluka and Guumilia are heading to the east (presumably to Snakeland in search of the twin swords). They come upon a country surrounded by a long wall, with a guard in front. The guard tells them that only locals are allowed to go through, and since the Magician Duo aren’t locals, they have to turn back. They obviously don’t give up that easily, and decide to disguise themselves by turning their hair black somehow. They come back, and the guard sees through their disguises and tells them their skin is too light. They go darken their skin with dirt and mud, come back, only for the guard to tell them that now their eyes are the wrong color. Elluka gets pissed off, and just summons up a wind to blow the guard away to who-knows-where. They go through the wall, and find that there was nothing on the other side, meaning the entire series of events had been utterly pointless. Eventually, however, they reach the sea.
In other words, Longwall and Watchman doesn’t deliver any worldshaking plot twists the same way MOTHellishY and the Muzzle of Nemesis do, it’s just a folkish song about an incredibly silly series of events involving Our Heroes. Nothing that would drop a bomb on fans the way the other songs would.