Had the same issue in VR.
Maybe the location of the files have changed since the last post on this topic but I had to fix this issue in a different manner than described above...
Here is how it worked for me:
Open up the following file (for standalone OB users) with your favorite editor:
DCS World OpenBeta\Scripts\UI\gameMessages.dlg
I searched for all strings containing:
["fontSize"] = *,
These values control the radio menu (I believe) and the server messages font size.
The default values stating ["fontSize"] = 20, are the ones controlling the message font size. I set this to 10 and that worked great for me (on rift S), 12 might give better readability.
An option in the GUI to go into sub 1 scaling (e.g. message scaling 0.5 and 0.75) would solve having to do this manually.
I would definately like to see the font scaling option in the GUI some day! ;)
Hope this helps anyone looking for a manual solution.
Cheers,
87th_Blade