The origin of the name Janis in Latvija is an ancient Latvian name. Its origins go well beyond the introduction of Christian names in Latvija. Janis is the name of one face of the great creator god, Dievs. It is likely a pre-Christian relative of the Janus/Jana, Dianus, Diana gods of ancient Rome and Greece. In other words, Janis represents the male face of god and Jana represents the female face of god.Jani Day - which is really a celebration of the Solstice and not of St. John, is a pretty good clue to how much this name precedes Christianity in Latvija.
Source: https://translate.google.com/?sl=en&tl=lv&text=Jānis&op=translate