The policy is that english is the language that is spoken by the staff and moderators, so content in english can be checked and moderated whereas informations in other languages can't be.
I'm not a native english-speaker myself, but I don't consider the "english-only" to be discriminatory, especially considering the communities page
that lists links to regional forums.
Scirra is aware that not everyone can speak english, but on the other hand, people have also to remember that Scirra is a small two-men company and that moderators are "volunteers".
We don't have ressources to handle different languages for now.
It's planned that tutorials would someday be available in different languages, and the very fact that the C2 IDE is to be translatable in the long term is another display that the "issue" is being considered anyway.