Using dictation feature to paste text into Terminal
This problem continued for me when I updated to 10.13.3 but I found a solution.  Rather than using the Paste Text option when creating the new Dictation Command, use the Paste Data command.  Then go to TextEdit and type the text you want, select, and copy it.  Then go back to the window creating your Dictation Command and click on the Import from Clipboard button.  You will notice that the button moves down (I assume meaning that there is data there now).  Now my Dictation Command works!  I am not sure if this works in earlier versions of Sierra.