1. Will be fixed in the next build.
2. True, but it's much easier to implement this way
3. Did you have the Manager open? It's a modal window so you cannot do anything with the other Rainlendar windows while it's open.
4. The manager doesn't show the end date if it's invalid or not defined at all. I'm not sure though what causes that in your case.
5. I had to make some compromises with the categories since combining everything from old Rainlendar, Outlook and Sunbird would have made the list too long (and it still is). Anyway, the ics-files are just text files so changing the strings can be done also with a text editor which probably is easier than with the calendar.
6. I tried with the latest German language file and they seemed to be ok...
7. Will be fixed in the next build.