On startup, the default locale is "C", meaning that all system
functions assume an ascii codeset. The environment's locale
settings should be selected by calling setlocale(LC_ALL,"").
This is done by Qt during the QCoreApplication initialization
but this inizialization is never performed for batch processing
and, as a result, LyX is not able to process files whose names
contain non-ascii characters. This is not an issue on Windows,
where the file names are always stored as UTF-16, so the call is
only performed for unix-like platforms (this also includes cygwin,
due to its own filenames management that allows using characters
which are forbidden to native programs).