Hi
I refer to the list you were linking to. I thought I would need to add the written variations of Romansh to this list, but found, that subtags were already made in 2010.
http://www.iana.org/assignments/language-subtag-registry/language-subtag-registry
If you look for Romansh, you’ll find 13 entries, and as written forms, the following 6:
Here you’ll find some more information to the topic:
https://www.iana.org/
With this provided information, I kindly ask you to open common voice for:
rumantsch puter
rumantsch sutsilvan
rumantsch surmiran
Thanks for your effort.