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Q: What happened to Frenchguycooking's/Alex's work?
A: His contributions and research are still here, and can be found unaltered in the page history. As of 18:19, Sunday, December 13, 2020 (UTC) they make up about 50% of the article's text, and they've been edited by 27 other people to varying extents. His research has proven valuable in uncovering the history of these classifications.
Q: Why doesn't the article say that mayonnaise is a mother sauce and hollandaise is not?
A: Truth is in the eye of the beholder, and more research is needed on historical and modern classifications. Most modern sources agree on the list given in the article's lead (introduction), and Wikipedia tends to follow the consensus of modern sources. While we should include the discrepancy between the original and the translation, it is not Wikipedia's job to declare, independently of modern sources, what is correct. Plus, it is noted that some modern sources do include mayonnaise.
Q: Didn't Escoffier consider mayonnaise one of the five mother sauces, and wasn't this messed up in translation?
A: The section Classification by Auguste Escoffier may help clarify some things. In the French version, Escoffier grouped four sauces (Espagnole, Velouté, Béchamel, Tomate) into "Grandes Sauces de base", and noted elsewhere that mayonnaise may be considered a mother sauce as well. In the English translation, Hollandaise is added to the group of four and they are dubbed the "leading sauces" or "mother sauces". We can only speculate why this is, but it's unlikely to be a simple translation error—it was likely intentional, either on the editors' or Escoffier's part.