Full Idea
Being able to ascribe the same proposition as a belief to persons who do not have a common language seems to be one of the main reasons to employ propositions.
Gist of Idea
We need propositions to ascribe the same beliefs to people with different languages
Source
Volker Halbach (Axiomatic Theories of Truth [2011], 2)
Book Reference
Halbach,Volker: 'Axiomatic Theories of Truth' [CUP 2011], p.11
A Reaction
Propositions concern beliefs, as well as sentence meanings. I would want to say that a dog and I could believe the same thing, and that is a non-linguistic reason to believe in propositions. Maybe 'translation' cuts out the proposition middleman?