@-axel-
I've uploaded a new version of the plugin, 1.1.1, which substitutes the current time if it can't parse the timestamp from My Clippings.txt. This will at least allow you to fetch your annotations.
If you want to try your hand at modifying the Kindle code, explode the plugin, find the document 'developer_notes.txt', follow the directions in step 4.
@chaley had a great suggestion - use the online translation service at
http://www.bing.com/translator to try to translate the line to English. This would assume an internet connection, and could be slow, as it would need to execute a translation for every annotation, but it could potentially solve the problem. There's a limit of 2MB of text per month through that site for free, so it would mean that individual users would need to have their own API key. This isn't something that I'm going to do in the near term, but you're welcome to try.
G