@brassel: Yes, the insel UI seems to be stable under Windows.
I still have trouble with the "i18nEntityType.properties". Although all changes in this file appear in the \AppData\Roaming\INSEL_8_3\customTypes\eu\insel\userblock folder, the properties do not show up in the insel UI. No difference if the block is created with the block wizard. Is there any solution yet?