chlori said:
I will be making a site in German and English. I'm not
sure, what language should be default.
In principle, the language selected from the preferences that the user's
browser sends. (It's non-trivial, since there can be several languages in
those settings, with different q(uality) values, and they may need to be
compared with the q values of the versions on the server.)
In practice, English, unless you expect a definite majority of visitors to
have German as their native language. The point is that English is so
widespread on the Web that nobody gets too surprised.
Pages like mozilla.org recognize my German Version
(Browser, Windows?) and suggest the download in German.
How do they do that?
I don't know. At least mozilla.org doesn't do it the right way: I don't get
the German version even if I put German topmost in my preferences. They
might play some guessing game based on top level domain. That's a wrong way
of doing things, though not fatal, if each language version has explicit
links that point to the other versions.
Do you think it's a good idea for sites to check the
language of the user and give them their language as
default (with the option to change)?
In principle yes. In practice, you need to be a bit enthusiastic to bother
doing so. For a bilingual sites, it is reasonable (but necessary) to have
explicit links that link the two sites together. More on this, and on
working with user's preferences, see
http://www.cs.tut.fi/~jkorpela/multi/
The main disadvantage is that the user's language preferences are often
wrong, typically just the language of the browser's user interface - and
even if it happens to be the user's first preference, it's hardly the only
one. Though, in fact, I have heard rumors that some people really know one
language only.