Google is the developer of the most popular web browser. If this is really a common problem, they can make UI changes to their browser to make that more accessible. It is not so hard to imagine a way to do it for even the most casual users, e.g. maybe using something similar to the Google Translate headers I notice when I use Chrome.

Besides, I have difficulty believing that this is a common problem. I have never seen a user whose OS was configured to a wrong language. Even if they have zero computer knowledge, they just ask someone else to fix it as the first thing. Computers/smartphones are already scary for technophobes; they wouldn't even touch them when they are in a language they don't understand.

This is especially irritating for VPN users as it is not just a problem when traveling, but all the time. I essentially gave up on hoping to get Google pages in a language that I understand. However, they made the situation worse in the past year: even if I use my country's localized Google domain, Google ignores that and gives me results according to my IP: websites from a different country about a possibly irrelevant subject, in a language I don't understand.