With core's Locale module you can enable Multilingual support for a content type. When creating/editing a node, this gives you a Language select list with all enabled languages and "Language neutral" as options.
The default (resp. first) value for this select list is always "Language neutral".
Is it possible to have a certain language as default value instead?
At best it would be a per-content-type setting, but I'm fine with a global one, too (e.g. always using the site-wide default language as default value).