What you get when a country tries to use any language that's not their native language, and makes mistakes in the process. That country is usually Japan in Danbooru's case, but other international screwups are possible and encountered. These mistakes can include both misspellings (such as the very common error of mixing up "L" and "R") and grammatical errors. Sometimes the speaker also is too young to speak his or her native language properly.
To find images containing this, search for the language name with ranguage.
Engrish is a well-defined and by far the most common form of ranguage and so gets its own tag.