Hi Harald,
Excellent work!
I've just made a quick joomla & jdiction install and it seems to work nicely.
The export function looks OK, but I'm having trouble importing the translations (tried both options, csv and xliff).
In fact, importing the file erased everything I had in the translated version (which I had created manually) and left it blank except for the title.
Also, after that, even though I manually entered a translation for the test page I created, it appears as untranslated (no green icon).
The site is not in the root directory, in case that matters.
I'm willing to help as a tester.
Best regards,
Leo