The most common and most likely answer to this crossword clue is the 8 plus 7 letter word AMERICAN ENGLISH
I've seen this crossword clue in The Times
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More clues leading to the result AMERICAN ENGLISH
Buddy explains!
The straight part
We know that "the words of Martin Luther King, say?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case the words of martin luther king, say? = american english.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.