In response to both Henrique and Periklis in:
http://lists.wfu.edu/pipermail/gretl-users/2018-February/012912.html
http://lists.wfu.edu/pipermail/gretl-users/2018-February/012909.html
It would probably be helpful if you could run gretl.exe with the
--debug flag and report what you see in the console box that
accompanies gretl in that case, when you're trying these operations
with non-ASCII filenames.
To do this you can either create a desktop shortcut to gretl and
append the --debug option flag in the Properties box (that's two
dashes at the start, before "debug") or you could invoke gretl with
that option from a cmd.exe window. This may give us more information
about the precise step in the processing of Windows filenames at
which the encoding problem arises.
Allin