I started getting the following error whenever i use SVN in my server:
svn: warning: cannot set LC_CTYPE locale
svn: warning: environment variable LC_CTYPE is UT
I found that combining several answers hear yields correct behavior.
This depends on what kinds of file names you have in your source tree. For example, I have english, hebrew and arabic. en_US.UTF-8 works for me "C" on it's own led to files which I couldn't update.