When you look around the comments here, you will see that while people agree on how this should be handled (list of languages spoken, in some preferential order) there is no consensus of where this should list come from.
It could be system - but there is a surprising amount of people who set their OS to some language they are learning, or just English for convenience. And they do not want this to affect the web.
It could be the browser, but YouTube and most other services for that matter, are mostly used through apps.
It could be in the profile (but which one Google, YouTube, local app?)
This seemingly simple problem has an issue with discoverability.
It could be system - but there is a surprising amount of people who set their OS to some language they are learning, or just English for convenience. And they do not want this to affect the web.
It could be the browser, but YouTube and most other services for that matter, are mostly used through apps.
It could be in the profile (but which one Google, YouTube, local app?)
This seemingly simple problem has an issue with discoverability.