What is the plural for “cul-de-sac”?

What is the plural for “cul-de-sac”?

What is the plural for “cul-de-sac”?

Culs-de-sac is correct. From French.

But, cul-de-sacs, although completely improper in French is now acceptable in English.

Language is not like math. No matter how often you are wrong in math, you are still wrong.
In language, if you are wrong long enough, you are right.