Ohh, boy, it went downhill fast.

Fantasy books already require a significant suspension of disbelief. The worlds are silly, but it's ok, because they're also wondrous and offer up adventures.
When there's interaction between three languages and new words are being made up and it's all just normal English, it's already a bit jarring, but fair enough, who wants to deal with con-langs anyway. I don't see the purpose yet, but all right.
Then there's inventing things from actual human history in a matter of weeks, deciphering dead language sounds from written text, training montages that aren't even montages... it diminishes the credibility of anything that happens this story, not to mention that these superpowers are treated as if that's just normal human things, compared to actual over powered magic.
This pushes the world from silly (in terms of being realistic) but fantastical into very, very obviously silly for all the wrong reasons.

But all right, it's a fantasy book, let the character interactions overshadow the flaws in realness, except there another annoyance of mine shows up. In an interaction between a teacher and a student, the teacher says that the way to overcome fear of failure is to find success. And I just find that wrong. In the real world, in training scenarios, you fail and fail again, the way you overcome fear of failure, is to realise that the world doesn't end when you fail, that it's not that bad to fail, that you can get up and try again, until finally you succeed. But this book is all about insta-success and I hate that. Oh, there's cost, but the cost is others, not your hard and boring work.