Tried to write some tags on moodle/tag/manage.php into Moodle 2.0 for a test.
I can't write tags that start with a german umlaut ÄÖÜ. My test words are Äpfel, Öre, Überzieher.
But it works with tags starting with an lowercase umlaut äpfel, öre, überzieher and with words with an umlaut in the middle Büro, Schlüssel, Stängel.
Another word with the german umlaut ß does not work: Straße
The error page comes with a link to error/moodle/dmlwriteexception
An additional error is that I can't write apfel and äpfel into the site tags ... there seems to be a problem that Moodle can't see that these words are different.