Translation:January is the first month of the year, and February the second.
Because February the second does not mean the second of February, it instead means that it is the second month of the year.
It's called ellipsis. When two sentences are joined like that and have otherwise parallel construction, key words in the second part can be omitted because they're understood to be the same as in the first part.
January is the first month of the year, and February [is] the second [month [of the year]].
In English, we would put a comma between "February" and "second" in order to show the ellipsis. Could this apply in Esperanto?
I wonder whether Zamenholf was aware of how months were named in East Asia. January is literally "month one", February is "month two", and it goes all the way up to "month 12". He could have named January "Unmonato", February "Dumonato", etc., rather than have their names derived from the Romance languages.
Perhaps, but Esperanto is pretty clearly a Eurolang, so going from there it makes sense that he'd name the months accordingly.
"La griza bruto de februaro."
I don't know why this made me think of the thief of always. Good book, need to read it again sometime. I wonder where if I still have it.