[“How oft the sight of means to do ill deeds
Makes ill deeds done.”
Shakespeare, King John, iv. 2.]

Latin

Latin de cuisine = Dog Latin.

J’y perds mon latin = I cannot make it out; I am nonplussed; I can make neither head nor tail of it.

Être au bout de son latin (or, rouleau) = To be at one’s wits’ end; Not to know what to do, or say, next.

Lettre

Je lui ai dit la chose en toutes lettres = I told him the matter plainly.

Ne prenez pas ce que je dis au pied de la lettre = Do not take what I say literally.

Lever

J’en lèverais la main = I would swear to it; I would take my oath to it.