We found a workaround for the OSX svn problem: You might want to add this small pre-commit script to your svn which checks for umlauts before commit and gives the user a warning:
#!/bin/sh
REPOS=“$1″
TXN=“$2″
SVNLOOK=/usr/bin/svnlook
## NOTE: This is a quick hack! WILL let many „dangerous“ characters pass!
if $SVNLOOK changed -t „$TXN“ „$REPOS“ | grep ‚^A.*\\195‘ >&2
then
echo „Auf diesem Server sind nur ASCII-Zeichen erlaubt!“. >&2
exit 1
fi
exit 0