World or Humanities rather depends on the exact spin you use in framing your quiz. If you focus on the English words, and use their Welsh derivation as a linking theme and as part of the extra information, it will belong in Humanities. If the questions focus on the Welsh origins, so they are really questions about Welsh or require knowledge of Welsh in order to answer them, it will belong in World. If you submit it to either category, the editor who sees it can let you know if it needs modification to fit there, or advise that it be moved because it will fit more smoothly in another spot.
I cannot answer you a bout the Author Challenge quiz - I have always avoided confronting the issue by not taking titles whose capitalisation bothered me.
(Editor in Humanities, Literature and Books For Children)
That's all, folks!