Hans,
here is a patch, copied from buff-imp-xml.lua, so that XML elements are
highlighted when they contain non-ASCII chars.
MWE that shows the issue (commenting the first line gives different
results):
\usemodule[scite]
\starttext
\startTEXpage[offset=1ex]
\type[option=xml]{<ans/>}
\type[option=xml]{<aáñs/>}
\stopTEXpage
\stoptext
Many thanks for your help,
Pablo