In the response on an OAI request DSpace does not send the characterset which is used. The German National Library (DNB) needs a correct charset to harvest the OAI interface.
This is the content type in the response header:
And this is what the DNB is expecting:
If the charset is not set, the DNB assumes the content to be ISO Latin 1 (and they told me this assumption is according to the standard).
I have corrected that locally in class org.dspace.xoai.DSpaceOAIDataProvider. But I guess it would be best to set the charset in a config file or detect the correct charset automatically.