<$button><$action-createtiddler $basetitle="myTiddler" tags="myTag" text="This is a text based on {{!!title}}"/>Create</$button>I understans the {{!!text}} in between the "quotes" along with your text is taken litreraly thus the text reference is not looked up.
If the button was in a macro you may be able to use "some text $moretext$ $(currentTiddler)$"
Or perhaps the new method <<__some var__>> can help but I have not played with that yet.
Regards
Tony
\define actions()
<$wikify name=tt text="This is a text based on {{!!title}}">
<$action-createtiddler $basetitle="myTiddler" tags="myTag" text=<<tt>>/>
</$wikify>
\end
<$button actions=<<actions>>>
Create
</$button>I may have a solution, not sure it's the smallest or the smartest ; and it uses the wikify widget.\define actions()
<$wikify name=tt text="This is a text based on {{!!title}}">
<$action-createtiddler $basetitle="myTiddler" tags="myTag" text=<<tt>>/>
</$wikify>
\end
<$button actions=<<actions>>>
Create
</$button>
\define actions()
<$action-createtiddler $basetitle="myTiddler" tags="myTag" text="This is a text based on $(currentTiddler)$"/>
\end
<$button actions=<<actions>>>Create</$button>