Life is happening through text messages. Facebook, Wechat, Line, Whatsapp, they are all ways that people text each other, and anywhere there is communication, there can also be language learning. In English language school classes students need to write 200-300 word essays, at university they can be as long as 5,000 words. But once people enter the workforce there is rarely need to write anything longer than an email, and usually they are only one paragraph if you are doing it right.
The reality is that most writing is in the form of short messages online. So it is worth practicing them from the start. When we meet someone and make contact, a regular text message through phone text is often the easiest, but as people become more friendly and closer they will use Facebook.
When I was in China I spent a lot of time on Wechat, the Facebook of China. I used to have my grammar and vocabulary notes next to me, and try to send texts to Chinese friends using that vocabulary and grammar. Whenever they responded with a word I didn't know, I would look for it in my dictionary and write it down carefully.
The language that regular native speakers use in text messages, is the most crucial language to learn.
Whatever people use in short messages must be absolutely essential - if you don't know it you must learn. The phrases that are taught in textbooks can never be as close to the heartbeat of a language as actual texting.