This is expected behavior. After installing and activating a plugin, you are supposed to Rebuild & Restart. There's a special button in the ACP to perform this.
Then there is no problem. Thank you for your answers.
Working Text2Speech working module available here
Note: Tested env Lavender(theme) & NodeBB v1.5.1.
-> Original Plugin has some issues and didn't work with nodebb , so i forked it and solved that bug.
Hurray - HappyCoding
@HARIOM-VASHISTH Do you have a screenshot?
Thanks owner of Text2Speech merged with my code. Now, Nodebb has working plugin.
Let's fix other plugins problems , also i am going to write an article about Nodebb deployment on ubuntu with http2 , https and Nginx.
@HARIOM-VASHISTH Nice work!
Oooh, text to speech, nice job! Invited you to join the 3rd party developers group.