Artem, Language exposure is a process that involves all areas [ listening, reading, speaking and writing] of language acquisition. The trick with language is exposure vs. acquisition. For example, a small child is exposed to language even while inside the womb, What has the small child acquired? Perhaps listening and speaking - even if this is babbling or cooing. After further exposure a child will acquire the ability to read and write. Very good question!

"Language exposure" broadly speaking, is to put yourself into an environment that encourages you to learn to use a language. Listening, reading, writing and speaking are the basic skills, but exposure means the right environment to use them. Think of speaking, listening, writing and reading as the basic tools you have. When you head out to a wild environment, then these are the tools you will need to survive.

Yes, it involves listening, speaking, reading & writing. It also depends on what level of proficiency you are looking for. What do you want to use that language for. If your main objective is to have a verbal conversation in that language then listening and speaking will do the trick. If your objective is to have a good command over the language then you should also concentrate on reading and writing. Language is primarily used for communication. Many people who know different languages may have limited exposure to some of the languages. It all depends on the person's requirement and usage of the language. Thanks!