I'd read it more generously than that. I think Chrome trying to stop the server choosing the language for you. By sending an accepts-language header (which your browser does regardless of what you use; it's not a Chrome thing) the server should return the page in a language you've said you'll accept. By adding the language to what you've told Chrome not to translate, it's attempting to show you pages in languages you want.
I imagine Chrome is really adding the language to your browser preferences when you choose not to translate a page, and the HTTP client in the browser is generating request headers based on your preferred languages. A small (and largely unimportant) semantic point, but it's possible that the Google translate team weren't aware of how adding a preferred language might impact user privacy. That isn't to excuse the behaviour; they should have checked.
I imagine Chrome is really adding the language to your browser preferences when you choose not to translate a page, and the HTTP client in the browser is generating request headers based on your preferred languages. A small (and largely unimportant) semantic point, but it's possible that the Google translate team weren't aware of how adding a preferred language might impact user privacy. That isn't to excuse the behaviour; they should have checked.