You do know what Bretons are, don't you? They're a Celtic people from northwestern France, from Brittany. In TES they're generically Western European with French, English, Spanish and Dutch names. Most of them have French names because Bretons are from France, regardless of the fact that they have their own language. Above all you have to remember that they can have whatever names that Bethesda wants them to have.
I know who the Bretons are IRL i have ancestors -its the correct word but it don't sound right- who Bretons... But if you look at the Breton characters from Arena and Daggefall, they mostly had very English sounding family names, then from MW onwards they suddenly had french names .
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Try going here to see what you can find http://www.uesp.net/wiki/Lore:Breton_Names
in fact that link backs me up.