Dear Garciat,
Replacong functions.php by the suggested version completely solved my problem. Thanks for your help!

After upgrading from 1.2.x to 1.3 I cannot see any content in pulldown boxes (administration - settings) for languages, styles and URL schemes although I have correctly installed languages and styles for the new version. It is not possible to change any other settings since the script displays error when leavin e.g. the language selection blank. However, in user preferences I can see and choose the installed languages correctly. What might be the problem?