[quitit]

While I used this example, which one could explain as intentional for various reasons. There are myriad other examples where there are dual languages being interwoven across google properties. Including minutia in one language, but the body content in another. Facebook/Meta's properties are the worst for this however and will intermingle languages frequently despite being an account-based service (literally ignoring the user's preferences in favour of IP-based guess work.)

Back to Google - Algorithmically there are likely straightforward reasons for why this is happening. Clearly the contents of the pages are composed from a mixture of sources, for reasons unknown these sources may not be able to detect or receive the localisation settings of the end user. Recent changes to privacy protections and cookie limitations may also be a contributor to these issues. Including the obvious: getting ads in the wrong language.