Only for the html5 module.
GMS_HTML5_TTS uses the vocal synthesis through the voices installed by default on your PC or related to the browser you are using. Online you will have more voices available than when you are offline, also depending on the browser used. Voices can have different accents for different languages or countries.
To make a voice say ' Hello World ', this simple code will suffice : scr_TTS_Play ( ' Hello World ' , false );
This version for GMS2 is an import of the GMS1.4 version. Keep in mind that the various tests were performed only on GMS 1.4 ( no longer having the html5 module for GMS2 ); This version is not a demo, it only contains the scripts and the extension. If you want the version for GMS 1.4 ( in gmz format ) you can find it for free on my site, as well as examples and related gmz files : https://www.gamequiz.altervista.org/Pages.php?Project=GMS_HTML5_TTS