Google TTS voice, I can't change the language

I need help. I have managed to get cast-web (v1.2.0) up and running and have my Google home showing up in ST. I have manged to write a script in webcore to get my google home to say something when a switch is activated. However I set the “use Google’s TTS voice?” to true and choose a “Google TTs language” to En-US which I assume is English and I get the “bleep” on the Google home device but no spoken words. Then in ST Settings I set the “use Google’s TTS voice?” to false and leave the “Google TTS language” as En-US and then the Google home speaks what I want it to say but in a foreign language i.e. Not english. Can anyone help me please.