Wrong, it's entirely realistic. This is just another masterful aspect of Star Trek's perfectly-depicted future history. Clearly Britain conquered France sometime during the Eugenics Wars, and in the general devastation, French language and culture disappeared and were replaced by British norms. Obviously.

I can't believe that you would imply that anything in Star Trek is unrealistic, poorly-thought-out, or poorly researched. It's literally perfect in every way. Obviously they thought this through and it's just one more strand in the rich tapestry of Star Tre- bahahahahaha sorry I couldn't keep it up