I seem to recall that Bujold mentions four primary culture groups on Barrayar: Russian, 'Greekies', and English, but I can't remember or find any mention of the fourth group.
The fourth group are the French
From "Captain Vorpatril's Alliance":
“Barrayaran Greekie?” asked Rish, brows rising in puzzlement.
“The smallest of our main languages,” he [Vorpatril] told her. “The Firsters actually arrived in four disparate settlement groups—Russian, British, French and Greek, as their home regions on Old Earth were back then. Over the centuries of the Time of Isolation, everyone pretty much blended together genetically...