So my questions stands now as: How can I use language strings in the description and how can I use different text for logged in users and guests.
You can't use multiple language strings anywhere in CB at once. You need to create 1 language string and use that language string as your description. Then in the definition of your language string you'd add your substitutions as needed. Example define usage as follows.
Code:
define( '_UE_MYLIST', 'Hello, [name] this is a userlist!' );
Then you'd add _UE_MYLIST as your userlist description. All places that use define usage can also use CBTxt usage assuming the string isn't defined so you could also do the following.
Code:
'Hello, [name] this is a userlist!' => 'Hello, [name] this is a userlist!'
Then use "Hello, [name] this is a userlist!" as your description.
Next to have descriptions with substitutions that are only used for login users you need to use IF substitution statements as follows.
[cb:if user="#me" user_id>"0"]I am logged in.[/cb:if]
See the below substitution tutorial for further information (IF substitution examples shown at bottom of page).
www.joomlapolis.com/support/tutorials/107-use-cases/18353-using-substitutions-throughout-cb