It baffles me that a ton of sites that have been translated into multiple languages still set the language based on IP rather than trying to determine it based on the client settings or defaulting to a set language with an easy way to switch it.

Countless times I landed on websites I use relatively frequently in foreign countries to see them in a language I don't understand, having to rely on my browser's translation functionality to find the language switcher. My operating system + browser are set to English, yet I still get served the one in the language I don't understand.

The worst offenders in my opinion are the ones assuming language based on IP for multi-lingual countries like Switzerland. People living in the French or Italian parts almost always get served the German content. It's bad UX.