.

Until this is fixed upstream, you can get around the issue by adding the following arguments when you launch the game: -Duser.country=US -Duser.language=en

On GDLauncher, you do this by right clicking the pack, selecting "Manage" and then turning on "Override Java Arguments" and adding them to the text box that appears.

This looks like a localisation issue, what language are you using?

I have reported this issue to the maintainer of RFToolsBuilder.