[[ https://en.wikipedia.org/wiki/Romansh_language | Romansh ]] is a language that seems to be spoken only in the Swiss canton of Grisons. MessagesRm do no have any fallback set, which means that [[ https://rm.wikipedia.org/wiki/Spezial:RecentChanges | rm.wikipedia ]] defaults to English, which is not any closer or similar to Romansh.
According to that Wikipedia article the closer languages would be [[ https://en.wikipedia.org/wiki/Friulian_language | Friulian ]] and [[ https://en.wikipedia.org/wiki/Ladin_language | Ladin ]]; with Italian being understood by all of the Romansh, Friulian and Ladin speakers.
Translation statistics for Romansh are in [[ https://translatewiki.net/wiki/Special:LanguageStats/rm | pretty bad state ]], and the same happens with fur and ladin ones.
As such I propose to set $fallback for rm to 'fur' and 'it', or simply set it to 'it'; as it is more likely that Romansh speakers understand Italian than English.
Another approach would be to, given that Romansh is spoken in Grisons, check which are the second and third most spoken languages there and add them as fallbacks so their inhabitants could understand untranslated messages better.
Best regards.