By AVGVSTA, in 'General Latin Chat (English)', Nov 21, 2018.
Is there a similar Roman festival or medieval feast?
supplicationes are days of thanksgiving to honor the victories of generals, not exactly the same thing though.
I don't know about possible similar feasts in the ancient or medieval world, but if you're interested in how to translate the thread title, here's my neological two cents: felicem tibi/vobis gratiarum actionem opto!
Maybe someone (not I now, because I'm going to bed) can search Google Books or so to try and find out if a phrase has been used for "thanksgiving" as a feast in neo-Latin before. Gratiarum actio seems the most likely candidate, because that's the translation of "thanksgiving" as, literally, the action of giving thanks.
The Morgan-Owens Neo-Latin Lexicon gives both gratiarum actio and gratulatio.
The Ludi Terentini, or "Secular Games" may be what you have in mind. Mind you, Augustus by way of the modern political partisan made himself pontifex maximus, and also held the aforementioned celebrations in the Campus Martius, which would last three days and three nights. Augustus (so we read in the contemporary Everitt), spent around $800,000 of his own funds on the Roman people, though the aediles were actually charged with running the events.
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