The language choice was because Ladybird started as a component of SerenityOS, which is also written in C++. With this separation, they are free to gradually introduce other language(s) into the codebase, and maybe eventually replace C++ entirely, piece by piece.
In Hackernews thread about this, the head maintainer mentioned that they have been evaluating several languages already, so we’ll see what the future brings.
In the meantime, let’s try to be mature about it, what do you say?