Language is a system that consists of the development, acquisition, maintenance and use of complex systems of communication, particularly the human ability to do so; and a language is any specific example of such a system.
Literature, most generically, is any body of written works. More restrictively, literature writing is considered to be an art form, or any single writing deemed to have artistic or intellectual value, often due to deploying language in ways that differ from ordinary usage.
The death of Dr. Hudson is a loss to the republick of letters.
William King, letter (Jan. 7, 1719). Same phrase occurs in the Spectator. Commonwealth of letters is used by Addison, Spectator, No. 529. Nov. 6, 1712.