As someone who makes extensive use of a DIY "immersive reading" approach to assist in learning two different languages, I will say here what I said elsewhere - TTS is VERY suboptimal (to be polite) for this purpose. The artificialities inherent in any machine-generated "speech" are not really a problem for an L1 speaker, but for someone learning a language, they can be a major hindrance. I do a lot of reading of Hindi material accompanied by a human narrator reading the same text, and it helps my comprehension and pronunciation quite a bit. I occasionally use Google Translate to "read" larger blocks of Hindi for which there is no human audio available, and the only gain is in hearing unfamiliar words pronounced. It's much harder to follow, even when the Hindi text Google "reads" is stuff that I've written. In the specific case of language learning TTS != "immersive reading"