Mischa Hooker has come up trumps and sent me a translation of the section of John the Lydian, On the Roman Months, book 4, which covers January! As with previous sections of John, this details the various Roman festivals in the month, together with other calendrical information, often from lost sources. Dr Hooker has also added copious footnotes. Here it is:
As usual, this material is public domain – use it in any way you like, personal, educational or commercial!