Am I the only one who is struggling with the fact that this language option doesn't speak and in most instances I can't review the word before it's quizzing me on it? Normally you can click on the gold and see the definition, but it'll send me into a situation where I can't do that and I end up, of course, getting it wrong.
Some basic rules will help you to "imagine" the sound, also: all the words are stressed in the penultimate syllable. All sylables that beging with "p", "t" or "k" sound like the "p", "t", "k" sound at the beginning of English words. All five vowels sound more or less like Spanish, clearly pronounced. At the beginning there is a section with all the pronunciation values and tips.
Also you can download Swahili recordings to accustom your ear to its sound. For example, there are some Bible recordings that you can download in https://www.faithcomesbyhearing.com/audio-bibles/download (be sure to look for Kiswahili, not for Swahili there).
The Wiktionary is also an indispensable companion while looking into meanings, etymology and the like.
Cheers and I hope that I have been of help.
There is a Duolingo userscript called Tree Enhancer, which adds TTS in some places where it wasn't available before.
It works over a script enabling browser extension, different for each browser. The instructions for installing it are in its GitHub site.
Sadly, the TTS voice for Swahili is one of the worst ones. But I really prefer to listen to it over not listening to anything at all.
It should be accepted (as should the student). Report it next time you see it.