Today I learned that the word sakoku 鎖国, referring to Japan's (generally exaggerated) self-imposed isolation during the Edo period, was coined by a translator at the interface between Japan and the West at the time. Here's what Wikipedia has to say about the word right now:

The term Sakoku originates from the work Sakoku-ron (鎖国論) written by Shitsuki Tadao [志筑忠雄] in 1801. Shitsuki invented the word while translating the works of the 17th century Dutch traveller Engelbert Kaempfer concerning Japan. The term most commonly used contemporaneously to refer to the policy was kaikin (海禁, Sea restriction).

So, Shizuki (for that is the preferred pronunciation, it seems) coined the word for use in the title of his translation. The obvious question: What was the original title?

Well, originally it was in Kaempfer's Amoenitates Exoticae, fascile II, volume 14. You can find the Latin on that page, but I learned it from GONOJI Masahiro 五之治昌比呂's On the Latin Original and the Translations of Kämpfer's Sakoku-ron ラテン語で読むケンペル「鎖国論」: 『廻国奇観』所収論文とその翻訳について:

Regnum Japoniae optima ratione, ab egressu civium, & exterarum gentium ingressu & communione, clausum

Which is to say, I believe, "The Kingdom of Japan which is, with optimal rationality, to the egress of its citizens & the ingress of external peoples & [any] communion [of the above two parties] closed." But it seems unlikely that Shizuki was working from the Latin text, and indeed SUGIMOTO Tsutomu 杉本つとむ in his Gogen kai 語源海 claims that Shizuki was working from the Dutch translation by Christian Wilhelm von Dohm (which, incidentally, was added as an appendix to his History of Japan, like this English version, which was probably where Shizuki encountered it). The relevant part of the Dutch is:

... 't Ryk van Japan om het zelve geslooten te houden

I.e., "The Kingdom of Japan which keeps itself shut up," I think (with a little help from Sugimoto's Japanese rendition). Sugimoto also quotes a comment from Shizuki about his translation:

此書元来は鎖国論といへる題号もなく、又上下巻の別もなし、是等はおのれが仮に設たるなり

This work did not originally have the title Sakoku ron, nor was it divided into two volumes; I have provisionally effected these changes myself.

But! When the work was republished in 1850 by KUROSAWA Okinamaro 黒沢翁満, he renamed it Ijin kyōfu den 異人恐怖伝, which put hiply is "Fear of foreigners." MATSUDA Kiyoshi has a page at the bottom of which he kindly gathered some comments from Kurosawa on why he undertook this rebranding; I have amended them slightly based on examination of the edition of Ijin kyōfu den linked above (hit volume three to check my work):

今世西洋舶来の書とて人々争ひて持栄す、かの国風に魂を奪はるヽ書の類にはあらで、此書は蘭人ケンブルが口より、正しく我大日本の国風を天下に比類なく善き国風なりと讃称へ又御国人の強きことを是も天下に比類なしと怖れ称へたる書なり、外国人の眼よりもさばかりに見ゆる御国に生れて却て彼が虚飾の威に惑されて恐るヽは愚味に遺憾き限りならずや [...] 此書は [...] 長崎の訳語家志筑忠雄が翻訳したるなり、当時書中の意を採りて仮に鎖国論と題号せしは、全く忠雄がわざなるよし訳例にいへれば、作者の意にもあらざる故に今又更めて異人恐怖伝と号けつ

Books imported from the West are so prized today that people compete for the honor of possessing them, and so lose their souls (tamashii 魂) to the customs of those countries (kuniburi 国風). This book is not of that type, but rather, a work in which the Dutchman Kaempfer correctly praises the excellence of our great Japan's national customs and the strength of its people as unequalled under the heavens. When this is clear even to the eyes of a foreigner about the country in which one was born, is it not foolish regretful in the extreme to be led astray and cower before the empty displays of vanity of that foreigner's country instead? [...] The book [...] was translated by Nagasaki linguist Shizuki Tadao, who, based on the contents of the work, gave it the provisional title Sakoku ron. This was entirely his doing, and as a translation does not convey what the author meant. For this reason I have renamed it Ijin kyōfu den.

As you may have guessed, Kurosawa was a kokugaku scholar. Invoking the authority of an imported book to support an argument that ideas should not be imported at all is a bit ironic, but I guess it beat writing his own argument. (And, of course, everyone knows about Japan's centuries-old love/hate relationship with foreigner approval.)

Bonus link: 近世後期日本における志筑忠雄訳『鎖国論』の受容 Acceptance of "Sakoku-ron" translated by Shizuki Tadao in last part of early modern times Japan, by Ōshima Akihide 大島明秀.