I noticed that the rules for language selection state
Your race indicates the languages your character can speak by default, and your background might give you access to one or more additional languages of your choice.
But a Druid's Druidic class feature says
You know Druidic, the secret language of druids. You can speak the language and use it to leave hidden messages.
And Speech of the woods:
At 2nd level, you learn to speak, read, and write Sylvan.
It seems there's no evidence that a character is literate in the languages they know (except for class granted ones that explicitly state this is so). Am I missing something? Being too pedantic?