Here's one thing you may be asking - do you want to know how to specify a join for n sources?
Yes. ‒ Your enquiry points into a direction for which I am looking also for further solution ideas.
for $e in $eng for $d in $deu for $u in $ukr for $h in $heb where $e/@n = $d/@n and $e/@n = $u/@n and $e/@n = $h/@n return <wf>{ $e, $d, $u, $h }</wf>
Will any improvements become relevant for the specification of such join conditions?
Regards, Markus