It is useful to know something of the manners of different nations, that we may be enabled to form a more correct judgment regarding our own, and be prevented from thinking that everything contrary to our customs is ridiculous and irrational, — a conclusion usually come to by those whose experience has been limited to their own country.

[Il est bon de savoir quelque chose des moeurs de divers peuples, afin de juger des nôtres plus sainement, et que nous ne pensions pas que tout ce qui est contre nos modes soit ridicule et contre raison, ainsi qu’ont coutume de faire ceux qui n’ont rien vu.]

René Descartes (1596-1650) French philosopher, mathematician

Discourse on Method [Discours de la méthode], Part 1 (1637) [tr. Veitch (1850)]
    (Source)

(Source (French)). Alternate translations:

It's good to know something of the manners of severall Nations, that we may not think that all things against our Mode are ridiculous or unreasonable, as those are wont to do, who have seen Nothing.
[Newcombe ed. (1649)]

It is good to know something of the customs of different peoples in order to judge more sanely of our own, and not to think that everything of a fashion not ours is absurd and contrary to reason, as do those who have seen nothing.
[tr. Haldane & Ross (1911)]

It is good to know something of the customs of various peoples, so that we may judge our own more soundly and not think that everything contrary to our own ways is ridiculous and irrational, as those who have seen nothing of the world ordinarily do.
[tr. Cottingham, Stoothoff (1985)]

It is well to know something of the manner of various peoples, in order more sanely to judge our own, and that we do not think that everything against our modes is ridiculous, and against reason, as those who have seen nothing are accustomed to think.