Why go
Language offers a useful clue to regional identity. Breton, Alsatian and Occitan point to histories that a standard French map label may not reveal. You do not need to speak them to notice their presence; recognizing that France has long been multilingual gives more meaning to a journey through Brittany, Alsace or the south.
The full story
French became dominant gradually. For much of the country's history, many people spoke regional languages at home. Public education conducted in French, urbanization and mass communication spread the national language, especially from the nineteenth century onward. That history explains why French is the shared language for travel today while regional languages still carry local significance. The contrast is easiest to understand through named regions. Breton belongs to Brittany, Alsatian to Alsace, and Occitan to parts of southern France. Their presence in regional culture and place names recalls a time when a journey across France could also mean crossing language boundaries. The overseas territories add further language histories beyond metropolitan France. Use French for ordinary travel exchanges, then pay attention to how a place describes its own heritage. A local name or language reference may tell you something about the region's past, but it does not imply that everyone nearby speaks that language now.