Haven’t tried the WIP yet but this would annoy me as well. Same situation, German system language but I use the default/English language for Rhino. I assume the vast majority of non-native-english users would use the Rhino with the default English setting, so this is a completely unnecessary way to annoy lots of users.
This bug was introduced when all languages were included in the single installer file on Windows. You can now switch languages without having to download a different installer. On macOS, it has always behaved this way.
-wim