The definition of moeurs in Trévoux is carefully written, and very broad:
MŒURS, s. f. plur. Façon de vivre, ou d’agir, bonne ou mauvaise ; habitudes naturelles, ou acquises, pour le bien, ou pour le mal, & suivant lesquelles les peuples, ou les particuliers, conduisent les actions de leur vie. Mores ; boni vel mali habitus mentis. […] Mœurs, signifie aussi, Coutume, usage, façon, manière de vivre grossière, ou polie. Mos, usus, agendi ratio. Nous prenons d’ordinaire les mœurs de ceux que nous fréquentons. Port-R.
It is notable that it is neutral, lending itself to either positive or negative uses. The definition in the Encyclopédie is rather similar:
MŒURS, s. f. (Morale) actions libres des hommes, naturelles ou acquises, bonnes ou mauvaises, susceptibles de regle & de direction. Leur variété chez les divers peuples du monde dépend du climat, de la religion, des lois, du gouvernement, des besoins, de l’éducation, des manieres & des exemples. A mesure que dans chaque nation une de ces causes agit avec plus de force, les autres lui cedent d’autant. (Ency.)
These definitions led me to think about two possibilities in English which I had not entertained earlier: behavior and habits. “Customs” would in principle do as well, but in L’Esprit des lois there are too many uses of coutûmes with a specific legal meaning. Habitude, however, is a word that does not occur in L’Esprit des lois, so it would not get in the way of some other line of reasoning. But maybe behavior would do even better, as a neutral term suiting a variety of contexts and also staying out of the way of most near-equivalents. There are so many passages that string together moeurs, manières, coutûmes and other terms that supposedly can be distinguished from each other.
But there were many occurrences of moeurs, and in many of them “behavior” either wasn’t a good syntactic fit or sounded strange. Then I hit upon “standards”, which has the advantage of having no obvious French equivalent, so it would not conflict with another word that occurred frequently in the translation. In practice I have often, for smoothness of context, preferred “norms”. At the moment that is the word of choice, except for one or two places where I could not square it with the context and reverted to “behavior”.