The internet loves dogs. Dogs love the internet. When the two try to communicate, you get DoggoLingo.
Doggos are cute, and thus must speak cutely. They are exuberant, laid-back, and eternally pro-social, and their language reflects this; a doggo may be a pupper or a thicc boi, a fluffer or floof, they may be a fren or a h*ckin' fren, but they all score at least 11/10. If you give a concern, they may bork or boof, but they will still hello fren you an' give you a boop.
DoggoLingo is closely related to LOL speak and Doge memage, but the odd grammar has picked up a lot of odd new words to go along with it. It started to appear around 2014, but the timing can't really be pinpointed, as it emerged from a widely distributed memesphere, with input from WeRateDogs, Dogspotting, 4chan, Reddit, and Tumblr, among others. While odd internet pseudolanguages are nebulous in definition, alternate spellings (e.g., birb, snek) and alternate nounings (e.g. danger noodle, trash panda) are often considered part of the lingo.
The core attributes of doggo are cute suffixes (e.g., doggo, fluffer), onomatopoeias (e.g., bork, mlem), and general milquetoastiness (e.g., flip h*ck!). And above all, pictures of cute animals, especially doggos.