Shouldn't God be capitalized?

I guess we have to discern two different concepts. There is (a) god (a concept that includes the possibility that there is more than one) and God (the one and only). I think the example sentence negates the existence of both monotheistic and polytheistic gods. That's why I would'nt capitalize here. — But at any rate I'm not a native speaker!

Indeed, and I can see that http://tatoeba.org/eng/sentences/show/3442053 uses "Dio". Should it really be "Dio"?

In my opinion, if we want to say "there is no one god of many gods, which many people believe in" we should say "There are no gods".
When we say "no God" we mean "there is no (one specific) God, which many people believe in". So, even atheists, who have no religious feelings, should capitalize it, cause it's a proper name.

I changed most of the translations; the Interlingua (which is further translated into German and then Afrikaans) ought to be split off.

I think this is not very meaningful to say "god" here.

"There is no god." would rather be "There is no god *here*."

However, I don't consider it a big mistake.
The Russian translation "Бога нет." is a bit ambiguous since the first letter is capitalized because it's the beginning of the sentence so we don't know whether it's God or a god.

"There is no God" is ambiguous. It can mean as "There is no God here" in a sertain place (Здесь нет Бога) as "God doesn't exist" (Бога нет).
If we write "god" (without capitalization) so I think it's similar to "There is no cat" (Здесь нет кошки). It means abcence of a (or the) cat in a sertain place, so "There is no god " can mean abcence of one of many gods in a sertain place?