(diggressing even further)
The case of the name of "Germany" in different languages is especially interesting:
https://en.wikipedia.org/wiki/Names_of_Germany
Basically there are 6 completely different origins for currently used names for Germany:
(1) one derived from an old high German word; this version is the source for "Deutschland" and is used in most German languages (except English)
(2) one derived from Latin / Greek which results in Germany, for example; except in English it's used in south-eastern European languages (e.g. Italian, Greek, Romanian, Russian ...) and languages that derived the name from the English word (e.g. Hindu, Malay ...).
(3) one derived from the name of the Alamanni tribe; this version is mostly used in western Europe (Spanish, French ...) and languages that imported this via Turkish (Turkish, Arabic, Tatar ...).
(4) one derived from the name of the Saxon tribe; this is basically used by Finnic languages (Finnish, Estonian and smaller groups)
(5) one derived from a Slavic term, used in eastern Europe (mostly in Slavic languages, but also in Hungarian; Turkish and Arabic use this term for Austria)
(6) one common among Latvian and Lithuanian languages
Regarding Nippon/Nihon and Japan: looking a bit over the Wikipedia article this seems to have to do with some complicated interactions between China and Japan and Europeans as early as Marco Polo were using some variations of names used in China. The Nippon -> Nihon change seems to have happened within the last couple of centuries (Wikipedia says in the Edo period, which means 17th to 19th century). Considering that both pronounciations are still in use (60-40 in favor of Nihon) and apparently younger people tend to use Nihon I would assume that 19th century is more realistic than 17th century.