While chatting on my Android (Opera / Chrome) I have no available voices to select from so I can’t use the speaking mode.
To clarify, are you talking about the Chat tab?: Readlang
The voices are provided by your browser and device so it could be that you need to install voices for the language you are learning via your Android settings. (I don’t use Android myself but you can search on Google for how to install more voices)
When I enter the chat, a pop-up window appears asking me to choose a voice, but no options to choose from appear—only the option to select the speed. If I click that, it rejects it, saying I have to choose a voice first. I use Firefox on Mac. Voices work during the practice session, although there was no opportunity to choose one.