The origins of French toast are not entirely clear, but long before this sweet snack was called “French toast,” similar recipes were being whipped up all around the world. One of the earliest versions of French toast has been traced back to the Roman Empire.
In France, the dish is called “pain perdu,” meaning “lost bread.” Why lost bread? Originally, people made French toast from stale bread in order to make use of bread that would otherwise have been thrown away.
French toast was not invented in France. In fact, French toast was around long before France even existed as a country. The exact origins of French toast are unknown, but it isn’t surprising that humans seem to have come up with the recipe quickly, given that French toast is traditionally made out of stale bread. Bread has been a staple food for most cultures since food first began being prepared and, up until very recently, the vast majority of humans would have never dreamed of wasting any food; thus, one has to find a way to make stale bread palatable. Soaking it in milk and egg and then cooking it, seems logical enough, making a good tasty meal while not wasting any bread.
Further, the name “French toast” pre-dates the 18th century, with the earliest references popping up in the mid-17th century, before the story of the grammatically inept Joesph French. Before that time, it was also known as German toast, Spanish toast, and a variety of other names, only some of which had anything to do with the name of a country.
North Americans call it French toast for very similar reasons as to why they call fried potato strips “French fries”. Simply that they were popularized in America by French immigrants.