Is it safe to say that "Jacka" should be pronounced more like "Dżaka" or "Dziaka"?
Okay, thanks. So, based on an exercise that came up soon afterwards, I noticed that the course is treating the English name "Jack" as equivalent to the Polish name "Jacek"; so if "Jacka" is treated as an inflected form of "Jacek", then the TTS pronunciation is correct.
From further research, though, it should be noted that "Jacek" is a modern form of the older Polish name "Jacenty", which is related to the names "Hyacinth" (originally from Greek), "Jacinto" (Spanish/Portuguese), "Giacinto" (Italian); whereas "Jack" in English is typically a diminutive form of "John", and sometimes of "James" and "Jacob". So, although they are being used as equivalents in the course, they are not directly related.
But then the given English translation has Jack, not Jacek.
Not the best example.