The languages currently available for text-to-speech on TextActivities are as follows:
Catalan, Chinese, Danish, Dutch, English (UK), English (US), English (Aus), Finnish, French, German, Greek, Hindi, Indonesian, Irish, Italian, Japanese, Korean, Latin, Malay, Norwegian, Polish, Portuguese, Portuguese (Br), Russian, Spanish, Spanish (Lat.Am.), Swedish, Thai, Turkish, Welsh
Some of these are of better quality than others. The TTS voices are provided by ResponsiveVoice, which uses Google's voices, and which, where possible, attempts to play speech using TTS engines integrated into the browser on your device.
If you wish to create resources for languages other than those listed above, you can still do so. Your resource will still have a wide range of interactive activity options, but all of those requiring interactions via TTS will be disabled.