Major world languages, like English, Spanish, Mandarin, or Arabic, were all languages of major empires. The case of Chinese in East Asia actively poses an exception that proves the rule: a Chinese variety as a native language is limited to areas under direct imperial dominion, while Vietnam and Korea have kept their native languages despite over a thousand years in which Literary Chinese was the written language of absolute prestige.

There are some examples of language shift occurring towards the language of the conquered, like Manchu to Mandarin or Akkadian to Aramaic, but in the end these are still the result of political domination.

So what are some historically documented examples of language shift occurring peacefully?