I thought it was kind of dumb. Why not just make the character british? A frenchman with a british accent really made no sense. It's not like Picard's french ancestry was vital to the story any more than british ancestry would have been.
I used to live in Spain, and I knew many Spanish people and French people who spoke flawless English with a British accent. Presumably the teaching techniques in the future are far superior to today and Picard obviously took advantage of those techniques whereas his brother apparently did not.
~String