Universal translators... We can't be completely sure where these people are from, unless they have specifically said where they are from, because their accents could be assigned randomly, or accents may be in the ears of the beholders, where users can tailor their user experience, or persons may be able to override personalizations, if they don't want to run the risk of being perceived as too sexy or too silly.
It's possible that Picard was speaking French, with a French accent the whole time on TNG, which makes a lot more sense than Jean-Luc speaking English with a British accent.