I've forwarded the details and reproduction steps, Markus!
There are a few labels in the administration that have been left without translation intentionally, but the reason is self explanatory. The ones that have been hardcoded are being chased after and provided to our translators. I'm not sure about an ETA, because performance optimizations are with higher priority right now (huge improvements are coming with 5.1), so stay in touch!
Grisha 'Greg' Karanikolov
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items