How to change "text to speech" accent?

I used to able to adjust the text to speech accent in the settings on a lesson page, just below the “options”. However, for some reason, the option to select the between them just isn’t on my settings tab, even when using the same lessons. It used to give me the choice between 2 different voices on Korean. Why is this option not available to select from on my new computer? I am using the same browser: chrome on macOS

For which study language you are unable to change the accent?