QSampler has bug, similar to JSampler bug #205 - it only opens, but doesn't properly pass filenames, whose paths include non-latin characters. Although now, with lscp 1.7, it's possible to pass everything up to lscp 1.7 (due to extended ascii allowed) - there is merge request at gitlab, that fixes (un)escaping for all lscp communications.
Still not best solution
(best would be to move (un)escaping under liblscp hood).
I guess, this could be closed, because it's now in master.