Correct, but one facet of xkcd passwords is that it's very easy to remember which prevents people from writing down passwords on sticky notes, thus eliminating

Correct, but one facet of xkcd passwords is that it's very easy to remember which prevents people from writing down passwords on sticky notes, thus eliminating that security risk. In the case of Welsh words, it's about as easy to remember for a non-Welsh speaker as leetspeak is, and so people will just write down the password somewhere again to remember it, which makes this less secure overall than xkcd passwords on English.