While we group our manuscripts according to their most important language, that does not necessarily mean that they only contain texts in that language. Most educated medieval people understood Latin, and some also understood other vernacular (?) languages besides their own. The manuscripts they read sometimes reflect this.
Likewise, the Geraardsbergen Manuscript is mostly made up of Dutch texts, but the collection of captions includes both Dutch and Latin ones, and the manuscript also contains a short French text, ‘Fol est qui fol boute’.
Our English manuscript, on the other hand, is a truly multilingual codex, thanks to an English scribe who decided to supplement a French romance with a ‘missing episode’ in English.
On the other hand, both MS germ. qu. 719 and MS germ. qu. 2370 are monolingual. Indeed, short verse narratives tend to be transmitted in monolingual contexts in the German-speaking area (as opposed, for instance, to religious texts or chronicles).