cannot attach files in sogo webmail with non ascii symbols in filename

Hello,
I noticed that I cannot attach files with non ascii symbols in filename using sogo webmail.
There is an entry in /var/log/sogo/sogo.log:
sogod[82818:12065535212040] EXCEPTION: <NSException: 0xaf9a8d06188> NAME:NSCharacterConversionException REASON:Can't get cString from Unicode string. INFO:(null)

After some googling I found out that sogo uses GNUstep as a dependency
and it requires the following envvar to be set for _sogo user:
$ export GNUSTEP_STRING_ENCODING=NSUTF8StringEncoding
When I launch sogo the following way:
su - _sogo -c 'GNUSTEP_STRING_ENCODING=NSUTF8StringEncoding sogod'
it works and there are no problems with adding attachments.
The question is: what is the best way to set this envvar for sogod
daemon so that I can control the sogod service using usual rcctl commands?
May be it would not harm to hardcode this setting in the package?

--
Maksim Rodin