Every man calls barbarous anything he is not accustomed to.

[Chacun appelle barbarie, ce qui n’est pas de son usage.]

Michel de Montaigne (1533-1592) French essayist

Essays, Book 1, ch. 30 (1.30), “Of Cannibals [Des Cannibales]” (1578) [tr. Screech (1987), 1.31]
    (Source)

Some translators use the 1588 sequence of chapters, not the 1595, and so identify this as ch. 31.

(Source (French)). Alternate translations:

Men call that barbarisme which is not common to them.
[tr. Florio (1603)]

Every one gives the title of barbarism to everything that is not in use in his own country.
[tr. Cotton (1686)]

Everyone gives the denomination of barbarism to what is not the custom of his country.
[tr. Friswell (1868)]

Every one gives the title of barbarism to everything that is not in use in his own country.
[tr. Cotton/Hazlitt (1877)]

Every one calls "barbarism" whatever he is not accustomed to.
[tr. Ives (1925), 1.31]

Each man calls barbarism whatever is not his own practice.
[tr. Frame (1943)]

Everyone calls barbarism what is not customary to him.
[ed. Rat (1958), 1.31]

Everyone calls what he is not accustomed to barbarity.
[tr. Atkinson/Sices (2012)]