No, I do not mean English versus French vs Swahili. I mean the right subset of your language for your audience.
Consider the extreme cases of presenting to a general audience of people in the public, versus a group of peer specialists. For latter you can easily use jargon and shorthand, because they know what you are talking about. For the former you need to use easy, everyday language, even if it means you have twist your technical topics a bit to explain the concept.
But what about, say, a conference which contains peer specialists, but also generalists from other fields, and managers who are definitely not specialists. – what then?
The trick here is to start off using the lowest common denominator in terms of language. Define those terms that you need if you will be re-using them. Perhaps, as a nod to the specialists you can throw in the technical jargon at points if it can help clarify a point for them, but does not interfere unduly with the rest of the presentation. The point here, though, is that you need to aim near the common denominator. The more advanced audience members will be able to translate up, but if you aim too high you will lose the rest of the audience.
The Speaking Scientist 