Babylon 5 is one of my favorite shows. I've got all 5 seasons on DVD plus the pilot episode and In the Beginning (tv movie). I don't have a few of the other movies yet, but they're on the list to pick up.
One of the many reasons I find this show so amazing is in how aliens might get confused when trying to use another race's idioms. Personally, I think I think this particular one is funnier by being wrong than what Londo intended to say. Remember when writing mixed race cultures that you think how races can muddle things up even when they have an excellent grasp of each other's language.
Getting things mixed up allows for moments of humor even in characters who are usually very serious. You don't have to give these sorts of lines only to the characters intended to be there for comedic relief. Londo himself is more of a tragic character considering his personal arc over the 5-year storyline. That's actually what makes the punchline in the first clip even funnier. He's so serious about it, and neither he nor his aide Vir realize the mistake they've made.
In the second clip, Londo is studying an Earth children's song, trying to make sense of it. Again, he's very serious and frustrated, and no humans are present to make fun of him for it. The only others in the scene are two Minbari: Delenn and Draal, and neither of them know the song either.