I agree that 'responsible' should not be used as a noun, despite that very strange OED entry, which reads like a bad translation from another language such as Spanish. Perhaps it came up in EU English somehow, before people started writing style guides.
Doesn't even 'responsible body' need some kind of marking or explanation? Is or was that term really used in the legal language of a particular English-speaking country or region, and if so, when and where?
In modern AE I would have expected maybe 'responsible party,' or else rephrasing with 'responsible' after the noun, e.g., 'the person/institution/etc. responsible.'
I can't imagine a context for 'body,' unless perhaps it referred to a legislative body, or a court of law, in the sense of having jurisdiction over a decision.
For Träger, Pons-Collins has senses such as '(der Kultur, Staatsgewalt, etc.) representative; (einer Bewegung, Entwicklung) upholder, supporter; (einer Veranstaltung) sponsor; (Mittel) vehicle; Träger einer Einrichtung sein - to be in charge of an institution.'
Is this perhaps like that last sense, and if so, would it perhaps be better just to include 'sein' in the phrase, like 'to be in charge / to be responsible'?