This AK::Format format system does not handle Unicode properly. An example (the same happens without a padding character):

outln("{:x>4s}", "a"); // outputs "xxxa"
outln("{:x>4s}", "©"); // outputs "xx©"

This is because the © (U+00A9) uses two bytes when encoded as UTF-8. Thus, the length measurement in FormatBuilder::put_string thinks the String has length two, and thus only prints two padding characters.

The immediate fix would be using Utf8View if the StringView is valid UTF-8, but I don't know if this has some other implications or if we should use a more general solution.