EGO, did you solve this issue? I also have problems with cyrillic (russian) letters when working with Zentyal 4.1 ans Samba, but not in group names, in file names:
2015/10/08 10:51:21 ERROR> Samba.pm:1045 EBox::Samba::_postServiceHook - Error setting security descriptor on file caramba/exchange/РазобÑаÑÑ Ð±Ð¾ÑвÑ/share/ÐÐ»Ñ ÐаÑи 14 ÑевÑалÑ/55182123_cupid01_as.jpg: Failed to open: NT_STATUS_ACCESS_DENIED at /usr/share/perl5/EBox/Samba.pm line 1043, <GEN0> line 940.
Seems that Samba accepts wrong encoding of non-latin symbols.