Accent vs. Dialect
Accent is how a person sounds when speaking. The sounds and intonations of your native language carries over when you speak a second language.
A dialect is the way people speak in different regions of the same country. It has a distinctive pronunciation and vocabulary. "Hey, hi yew" is southern speak for "Hi, how are you?"
A southern accent, a Boston accent, a New York accent, a mid west accent are all very distinct but are still American English.
Whether you are presenting to a few in a board room or hundreds in a ballroom if your audience can't understand you they will tune you out no matter how great your content.