A lot of web sites are translated in many languages. And when we visit them, they usually look up at our web browser's language preferences (locale). However, the content differs between languages and not everything is translated. For example, my home university's web site has a lot of content in Slovenian but only essential information in Italian and English. So I would like my browser to show me the Slovenian version of it. But I want Google in English, because I don't get it in Slovenian. If I set my language preferences to Slovenian, Google gets translated as well; if I set it to English, university's site shows up in English and I have to navigate to the language I like. Google for example, has a preference form when one can select the preferred language. But in my case it keeps changing back to my locale after some time and I have to do it over and over again.
Some web sites look also at user's IP address and show the content accordingly to IP's geographical location. This gets even more annoying than browser's locale. When traveling in Germany I still want my web pages in English as I might not speak German :).
I know this is not a problem to native English speakers and that it is not hard to just select a right language here and there. But it produces a few undesired clicks.
So why not having a per-site language settings besides a global one? I might be the only one just slightly annoyed by this issue! But on the other hand, I never officially complained to the browsers' people :). I have to do that.