What is french for let alone?

The French equivalent of "let alone" depends on the context:

1. To express impossibility:

* sans parler de... - literally translates to "without speaking of..."

* à plus forte raison... - means "all the more reason..."

* ne parler même pas de... - literally translates to "don't even talk about..."

Example:

* "I can't even afford a coffee, let alone a new car."

* Je n'ai même pas les moyens de me payer un café, sans parler d'une nouvelle voiture. (I don't even have the means to buy myself a coffee, let alone a new car.)

2. To emphasize the impossibility of a second action:

* à fortiori... - similar to "all the more reason..." but more formal.

* d'autant plus que... - means "all the more so because..."

Example:

* "She can't even walk, let alone run."

* Elle ne peut même pas marcher, à fortiori courir. (She can't even walk, let alone run.)

3. To express something unexpected:

* sans compter... - means "not to mention..."

* sans oublier... - means "not forgetting..."

Example:

* "The food was delicious, let alone the service."

* La nourriture était délicieuse, sans oublier le service. (The food was delicious, not to mention the service.)

The best choice will depend on the specific context of your sentence.