"The educated Southerner has no use for an 'R', except at the beginning of a word"

Mark Twain's quote is a humorous method of mentioning the Southern dialect of English. In the South, the letter "R" is frequently dropped from the end of words, such as "concept" ending up being "idea". This is a function of the Southern dialect that is typically viewed as an indication of lower education. By saying that the informed Southerner has no use for an "R", Twain is suggesting that the educated Southerner speaks in a more standard type of English, without dropping the "R" from completion of words. This quote is an amusing way of mentioning the differences between the Southern dialect and the more basic form of English. It is also a suggestion that education can have a significant effect on the method we speak.