In a nutshell: YouTube has been working on multi-language audio support publicly since at least 2023, and perhaps for several years longer behind the scenes. The actual timeline doesn't really matter because now, Google is expanding the feature to millions of additional creators.

YouTube Product Manager Ritz Campbell said that over the coming weeks, creators across the US will have the ability to leverage the new feature. Within moments of a new video going live in English, viewers in other countries like India or Brazil will be able to watch it in their native language.
YouTube has already demonstrated that multi-language audio has massive potential. In early 2023, the video sharing site said it had worked with MrBeast and a handful of other content creators to trial the budding feature. Since then, on average, creators who uploaded multi-language audio tracks to their videos saw more than 25 percent of their watch time come from viewers watching in a non-primary language.
Some creators, including former NASA engineer Mark Rober, are fully invested in the new feature. Some of his videos have an average of over 30 audio dubs. Chef Jamie Oliver, meanwhile, has seen multi-language audio boost views by more than 3x.
For most creators, there's little reason not to utilize the new language tools. It allows creators to expand their global reach to regions and cultures they have likely never even heard of, all while boosting traffic and in turn, generating more ad revenue. The feature also results in more diversity in the comments section – all helping Google continue to grow one of its most lucrative investments.
For someone like MrBeast with 434 million subscribers or Mark Rober with 71 million followers, those extra views can translate to big bucks. But even for those just getting started with content creation, there's plenty of upside. Perhaps the handful of extra views one might receive through multi-language audio dubs could be what motivates them to keep going instead of throwing in the towel. After all, everyone starts at the same place in the beginning.
YouTube is also piloting localized thumbnails based on a viewer's selected language.
YouTube rolls out multi-language audio dubbing to millions more creators