Part of every lawyer’s job is communicating—either explaining options and risks to the client, or persuading a judge or adversary of the merits of a case. They should be well-spoken, and willing to communicate effectively on your level.
Lawyers who hide behind legal jargon may be quite competent, but they may also be hiding their incompetence behind a lot of words that non-lawyers and other normal people would never use in ordinary conversation. If a lawyer cannot explain legal concepts to you in language that you can readily understand, it is likely that he does not understand it very well, himself.
Lawyers often need to use jargon in court, when dealing with other judges or other lawyers; there is rarely a need to do so with a client.