I believe this is another case of 0006494, which will be fixed in Mantis 1.1.0 by using UTF-8 instead of separate character encodings for each language. You can use a release candidate of Mantis 1.1.0 already, if you would like and don't mind that it's not a final release. You would have to manually convert your database tables to UTF-8 though.

Thank you for taking the time to report a problem with mantis.

Since this problem report was originally made, a number of releases have occured.
It appears that this issue has either been fixed, or may not be a relevant report for the current release.

Unfortunately you are not using the latest version and the problem might already be fixed. Please download the latest release from http://www.mantisbt.org/download.php [^] [^]

If you are able to reproduce this bug in the current release, or have some more information on how this feature could be improved in the current release. Please either change the mantis version on this bug report
to the version you tested and change the status back to "Open", or open a new issue report with more information.

Again, thank you for your continued support and report.