The most basic, and all encompassing definition of Language Arts is Reading and Writing (Composition). Reading, particularly dramatic reading and poetry reading, is an art, one well-known to parents of toddlers who want bedtime oration. Composing, of course, includes virtually all the written skills learnable, including -but not limited to- technical writing, copywriting, persuasive, speech-writing, essay, short-story, novel... oh, yes, and ARTICLE writing!
Although writing followed speech by several hundred-thousand years, writing and written language arts hold a special place in learning, teaching and the entertainment professions today. Media giant Marshall McLuhan once famously quipped, "The person who says entertainment has nothing to do with education does not know the first thing about either!"
Language arts, then, encompass almost any form of moving the printed message out to an audience, whether that audience is one, (YOU, the reader) or a roomful of avid fans or a theater full of paying customers... the idea is the same as a teacher, pausing for dramatic effect: present the message in a non-monotone, non-boring way. Teachers who ignore this part of instruction show that they do not, in truth, understand the first thing about education: present your information in an entertaining manner, to improve receptivity of your audience and to increase uptake, absorption and retention among those listeners.
The human nervous system responds to CHANGE, and stops sending signals when there's no CHANGE of input signal. That's why a steady stream of monotonous, unvaried, unbroken, uninterrupted words can put us to sleep as quickly as a warm bath or a ticking clock. No change!
Hence the language arts are the ways in which we use language, written and spoken, to touch, move and inspire listeners, even when they are students who must come to class! A monologue or a dramatic reading allows one person to bring a particular thought or series of thoughts to the listeners in a way which may sway and influence the listeners in a pre-determined manner.
Poetry, not quite music, still sings to the listener in a way which lifts the ordinary words up to the level of art, using rhythm and rhyme in ways that slip extra meaning past the listener's conscious mind and move language arts to the heart of the sharing. Poetry, then, lends itself to the musician, who adds yet another layer of meaningful nacre to the pearl of meaning established by the poet and enlarged by the reader.
Role-playing is an art which helps learners master the language arts, as is memorizing a dialog, first for the A speaker, then for the B part. Such memorization can be an essential part of language learning, and develops not only the learner's language art but also the learner's memory and mnemonic capacity.
Language arts, then, are the different ways we turn language into entertainment, lift language from the mundane to the sublime and by so doing, elevate ourselves and our language to the near-divine!