You've probably answered these questions several times already.
yes, I did but I'll answer you very briefly.
If God doesn't care, why does he actively threaten/warn about Hell in the scriptures?
Although His infinite majesty makes Him not care, He's still infinitely merciful as well. He doesn't really want Hell for me, so He warns me against it... if I don't care for His warnings, he won't care for me.
Seems to me the intention of Hell is to frighten people (which works very well).
That's very plausible (Hell being an invention to frighten people).
If the Prophet was meant for all people, how come after 1400 years it is still almost non-existant in South America?
So what? Are you saying that South America isn't aware of Islam?
Why was the message presented in a language that seems to be impossible to translate?
The message itself can be translated, though.
If not knowing the true message excuses you from an eternity of Hell, why not burn every single Quran and completely obliterate Islam so that all who follow us are completely ignorant of it, thereby saving all those who don't believe from an eternity in Hell? That way people would be judged by the merit of their action instead of their blind belief in what happened to be the true religion.
It's like saying instead of making the Law known, why not hide it, so that people can repeatedly break it without being held accountable.
If God didn't want us to be accountable, He could have created us as the rest of dumb animals.
Why would you expect God would want to hide His truth from us? Heck, I can even ask a better question: Why didn't God just create more angels, instead of creating men, capable of war, blasphemy and evil? The angels did ask God that question in the Quran, and God said only He knows why He created man with the ability to choose.