While creating new content with translation different than default there is a problem with embedded content - it doesn't have first declared for siteaccess translation set as default.
Creating new content without using "Content on the fly" takes first declared language for siteaccess.

Steps to reproduce
1. Create new language in admin panel via PlatformUI
2. Create new content using this new language
3. Try to embed a content in RichText field by creating another content
4. Notice that default language of embedded content doesn't match its parents'

v2.0 isn't affected due lack of "Content on the fly" functionality.