Include macro doesn't support translated documents

This is a regression. This issue was first fixed in XWIKI-2892. The regression was introduced in XWIKI-5807 during a refactoring.

Basically the call to DAB.getDocumentContent() was replaced by a call to DAB.getDocument().getXDOM() because getDocumentContent is a deprecated API. The problem is that DAB.getDocumentContent supports translated documents thanks to XWIKI-2934 but DAB.getDocument doesn't!