Although "In dulci jubilo" appears to have been macaronic (Latin-German, to be precise) at its creation, and although there exist many macaronic versions of it that substitute another language for the German while retaining the Latin, there are also many monolingual versions. Here is the monolingual Latin version from ingeb.org:

---

1. In dulci iubilo
   cantate domino
   nostri cordis gaudium
   in praesaepio
   et fulget ut lux solis
   in matris gremio
   |: ergo merito :|
   iubilizat cor omne
   mentis tripudio


2. O Jesu parvule
   langueo post te
   laetum fac cor meum
   tu puer optime
   et tuum fer auxilium
   tu puer inclite
   |: trahe me post te :|
   ad regnum patris tui
   tu princeps gloriae


3. Ubi sunt gaudia
   plena gloria
   ubi canunt angeli
   di nova cantica
   nam sonat vox laetitiae
   in regis curia
   |: eia qualia :|
   laetam mentem faciat
   Christi praesentia


4. Maria nostra spes
   da, virgo nobilis,
   ne nos repellat fragiles
   tua progenies :|
   nostra dele peccamina
   laudanda species
   |: vitam nobis des :|
   et nostra sit hereditas
   aeterna requies

---

I'm not sure how the last two lines of each verse are handled, coming as they do after what in the tune as I know it is the end.

Haruo