Translated wysiwyg were not stored correctly in database (before JCR time) as translations
Thus you could have many wysiwyg for a singe publication each with its own language extension.
So now if a wysiwyg has not language defined in database, we use the extension to compute the real language of the content.
When we have different wysiwyg attachmentswith the same name (except for the _lang extension) we merge them in a single SimpleDocument, eachbeing a translation.