Hm a little bit late to answer, does the issue persists?
I guess, it can't work in this form.
The joomla core language file calls de-ST.php, and the same is in CB language file and folder.
But the joomla core language files for german are de-DE.
ini and in CB language file and folder, they are NOT de-De, but german (folder), german.xml and german.php.
Maybe this are international norms (don't know exactly), everywhere and always it is de-DE.ini and is called in programs german, same for France: fr-FR -> french and so on.
This is, where CB looks for: What language is set in Joomla, and if the same language file exists for CB it uses this language, in the other case it uses the default language = english.
And Joomla needs the ini files de-DE. I did never use joomfish, but I guess there are also needed ini files (joomla language) to work.