Zimmerman was acquitted of killing Trayvon Martin because the crucial witness spoke a strongly nonstandard dialect of English, typically found among blacks, and the jurors interpreted her testimony wrong by taking it as standard English.

More analysis confirming that Rachel Jeantel spoke in a typical form of African-American Vernacular English, though with a little influence from Haitian Kreyol, and that she consistently followed the grammatical and lexical rules of her dialect. The jurors (none of whom knew that dialect) frequently misunderstood her testimony.

I support the idea that courts should use interpreters whenever witnesses appear to be speaking in a dialect that many jurors will not understand.

This also demonstrates how important it is for everyone in the US to learn to speak a more standard form of English — standard enough that you won't be systematically misunderstood. Not that you shouldn't ever speak some other dialect that you grew up with — but don't let that be the only one you can use fluently.