Amen brother. That is one of the most annoying things I know - it actually bugs me more than popup ads do. I seem to recall that SourceForge and Debian are among the offenders, and thereby sites I rather avoid. Especially Debian really sucks, because even if I choose a new language (English, as it were), it forgets this as soon as I click a link.
I want an opt-in solution for this kind of things, and preferable English as the main language. I am Swedish, but I don't usually appreciate translations, even if they are good, lots of context is lost in translations. And technical stuff is rarely suitable for translation at all, IMHO. Since so much of the technical lingo is English or derived directly from it, "thinking" in one language at the time is enough, thank you very much.
Yeah, this is only how I feel about it. But I do so strongly. :)
And yes, I never buy translated books either, not for fiction, nor for fact.
You have moved into a dark place.
It is pitch black. You are likely to be eaten by a grue.