Excerpt taken from the book The Story of French (Ch. 1)
The Gaulish language ended up contributing very little to the vocabulary of modern French. Only about a hundred Gaulish words survived the centuries, mostly rural and agricultural terms such as bouleau (birch), sapin (fir), lotte (monkfish), mouton (sheep), charrue (plow), sillon (furrow), lande (moor) and boue (mud)—that’s eight percent of the total. However, Gaulish is still relatively well-known, partly because it left many place and family names in northern France. For example, the name Paris comes from the Parisii, a Gaulish tribe, and the word bituriges (which meant “kings of the world”) produced the names Bourges and Berry (the difference comes from whether the original name was pronounced with a Latin or a Gaulish accent). Linguists believe that Gaulish also contributed to development of the peculiar sonority of French, and that it was at the root of some important linguistic variations in what would become French. But, contrary to what some people believe, modern French is not Latin pronounced with a Gaulish accent.
The Roman occupation spawned a new language that would play an important role in the formation of modern French. In the Roman province of Gaul only one percent of the population was literate, and those who wrote used Latin. The rest of the population spoke a rustic, popular “street” Latin that would come to be known as Gallo-Roman. By the fourth or fifth century ce, Gaulish had all but disappeared, though a few speakers stuck it out in Normandy until about the ninth century. (The Celtic language spoken in Brittany today was actually imported by Celts who fled to Brittany from Britannia in the fifth and sixth centuries ce, to escape the barbarian invasions.)
Gallo-Roman went on to have more lasting power than the Roman Empire, which crumbled in the fifth century ce. Germanic “barbarians” (a Greek term referring to peoples who don’t speak Greek; any other language sounded like “bar-bar” to them) had already been invading Gaul for a century. Tribes including the Vandals, Goths, Saxons and Vikings all settled in different areas of France, where they intermarried with the inhabitants. Curiously, although the invaders left important traces of their language wherever they settled, they all picked up the local Gallo-Roman dialect. This created a galaxy of different dialects across what would become French territory, all of which shared many words and characteristics.