Do you remember this post you LITERALLY just made?
So, why do we need starvation rules? Why can't we just make them up? You've stated we don't need the MM, because we can make things up, well, why can't we make up classes, ancestries, and rules for starvation and difficult terrain? You apply one standard to one book, then another standard to the other book, with no rationale except "but this book said that book has rules in it"
You keep saying they aren't rulebooks so... yes, you have both said and implied that the DMG and MM are not Core Rule Books, and then you felt specific need to mention splatbooks, which would be the only other type of book you could refer to those two as.
Nowhere in any official material has it ever been stated that no rules for the game exist outside of the PHB. You have never explained why the Burrowing Rules are different from any other rule, except that they exist in the MM and therefore you refuse to except they are rules.
I have explained this. The DMG paragraph does not state that the only rules in the entire game of Dungeons and Dragons exist in the PHB and nowhere else. It states the rules to run the game are in the PHB, which is true, because the PHB covers the basics of D20 tests which are fundamental to the running of the game. That does not mean that literally everything else is a mere "guideline"
The Language of the Gods contains mystical words. The Language of Fire contains Mystical words. The language of entropy and evil contains Mystical words. RAW's requirement is met.
No. Everyone can roll it. Not everyone is trained in Arcana. Training in Arcana is represented by Proficiency in the skill.
No where in the ability to counterspell does it give you special knowledge of words and tones. Nor does Counterspell require you to have used magic, or be a sorcerer. You are continually making things up.
Nothing about NOT SCREAMING LIKE A FOOL!!! requires a special rule.