Umbraco 4.7.1.1. We have a number of sites under one installation. Each site has it's own hostname. There are mutiple users, each with different languages assigned as they operate from around the globe.

In the richtext editor, the right click menu shows: "{#undefined}" next to Cut, "Kopieren" next to Copy, and "Plakken" next to Paste. But beneat that the other options like Alignment are in English. This is for all users, including the main admin user (me) who has "English (uk)" language assigned. Why would these get mixed up like this? Could I re-install a language file or something similar?

Similarly, when logging out of Umbraco the message says: "Ben je zeker?" rather than "Are you sure?". This makes me think it isn't specific to the editor, but a more general issue, even though all other menus, etc seem to be displaying in English.

How can I troubleshoot this issue? I understand that there may not be anyone who knows the solution, but a nudge in the right direction would be a huge help.