Hmm, borrowing papers seems to be becoming something of a point of conflict within the Faculty.
The Old English paper (under the umberella of 'Paper 7', in which all languages, except English Language [Paper 8] are contained) is not a borrowed paper; rather, it is a paper written by the English Faculty for English students. Though we cover much the same material as the ASNaC Anglo-Saxonists, our paper is more literary and less linguistic (though there's certainly an unavoidable element of the latter, much to my distress!). This is the same, I believe, for all languages in Part I: they are specifically English papers, rather than borrowed from other Triposes.
It tends to be in Part II (3rd yr) that papers are more freely borrowed. Though quite how much freedom is arguable and contentious. Theoretically, however, it's possible to do Old Norse and Renaissance Latin (is that the same as Insular Latin, Lidia?) -- I know people doing these options at the moment. There used to be quite a long list of papers we could borrow, including from the History, MML (about which you could ask Da Bachtopus, who borrowed a French paper at Part II and is now studying in France), Linguistics and ASNaC Triposes, but I don't know to what extent these are now available. The difficulty with borrowing seems to be because the disciplines require different skills, and the Faculties have to feel sure that the person borrowing the paper will not drag either facultys' marks down. Think of that what you will.
There is one other option to replace Paper 7 language: Paper 10. This covers the gap between 1066-1300, that Tripos doesn't otherwise do. This is quite a funky paper, and you have to do two of three languages/literatures within it -- Medieval English, Medieval Latin, and Medieval French. This is quite a funky paper, and I would have taken it had I known of its existence. (It's only subjectively funky, though -- no better or worse than any other paper, technically!).