There is no proficiency. Mystic words are mystic words. They're mystic whether you are trained or untrained, a caster or non-caster. If you like though, you can require the PC to have arcana. Oh, right, PCs already have all skills whether proficient or not. So pick any skill you can think of and the PC has it and will recognize mystic words.
So, you declare they are recognized by "anyone with the training" which would imply proficiency, and now they are just recognized because they are recognized with no training? And the language of Fire isn't a mystical language? You never explained that actually, what makes the Language of Fire NOT a mystical language?
Incorrect. What it means that is even with a 3 int you can recognize mystic words when you hear them. Nothing about a 3 int by RAW means you can't recognize such words. You have one specific beats general example of a 1 int being unable to do it, but nothing by RAW says even a 1 int acquired another way will prevent the PC from understanding the words.
Nothing in any books says that Int 3 can recognize words. In fact, many creatures with an INT 3 specifically do not understand any language. So, this reads like special pleading for the thing you made up to just have the exact properties you need it to have.
So tell me. How do you know you are seeing a creature cast the spell if you don't know what the words are? Something has to tell you so that you can counterspell.
Nobody is going to just walk around launching random counterspells without knowing a spell is being cast, which is what you are arguing by saying you don't need to know it's casting a spell.
I do not know how you know, it is a function of magic. The rules simply state that I know. You cannot claim that knowing the words is required because
1) There is no requirement that counterspell can only be used by a caster or someone with spellcasting. A creature with a boon or a magical item could still cast counterspell.
2) There is no requirement to hear a spell being cast. Deaf creatures can counterspell.
3) There is no requirement to understand what spellcasting is, extreme low INT beings can still utilize Counterspell.
You can make these incorrect claims until you are blue in the face, but until you can show that the DMG is lying, you are wrong. Can you show the DMG statement to be a lie?
They are a suggestion because they are a suggestion. Can you show the DMG statement to be a lie?
Can you show the DMG statement to be a lie?
I do not need to show that the DMG is lying. That is ludicrous. The PHB contains the general, baseline rules, this is true. The Monster Manual contains monsters, this is also true. The Monster Manual ADDITIONALLY contains rules. The rules for the monsters, which are contained in the Monster Manual.
Using the PHB, you cannot describe how a Burrow Speed works.
Using the PHB, you cannot describe how Tremorsense works.
Using the PHB, you cannot describe how Proficiency works for creatures that do not have Levels.
Using the PHB, you cannot describe how a mid-combat recharge of an ability using a die works.
These are rules. These are very explicitly rules. Just like the rules in the PHB for swimming, darkvision, short rest recharges and proficiency by level.
But you do need to know what it is in order to cast, "Destroy Iso-Flux." If you didn't know what one was, would you cast it every time you saw something you didn't know about? No, you wouldn't.
If it states that when I see an Iso-Flux activating, I can cast this spell to destroy it, then I can. There is no requirement to know what it looks like.
You also cannot cast a reaction spell that does not have the proper trigger. A player can't declare they cast shield when someone walks over to them. The trigger is not met, so the spell cannot be cast.
There's already an optional rule for that and it takes your reaction. It's also yet ANOTHER strawman to claim I'm saying that they need to ID the spell.
OH!!! Since you've successfully argued that splatbooks are RAW, yes your Strawman does work that way by RAW. By RAW you need to spend your reaction and make a roll in order to ID the spell. See Xanathar's.
Yes, if I choose to use that rule, it would work that way to identify the nature of the spell. How would I know to use my reaction to try and discern the nature of the spellcasting, if I am deaf and otherwise would have no idea what I am looking at? Would I still be able to make the attempt?
By your standards.. no, I would not. If I were deaf, I would be incapable of identifying a spell. However, yet again, this requirement is not in the Xanathar's rules. You simply need to see the creature.
And yet according to you, someone would be revealed as casting a spell despite doing absolutely nothing to indicate that it is casting a spell. Absolutely nothing. Because moving lips do not indicate spellcasting. That's essentially perfect knowledge.
If they are casting a spell, they are not doing nothing. They are casting a spell. And the counterspell can be activated when you see a creature casting a spell. If moving your lips to move your lips, you are not spellcasting. If moving your lips to spellcast, you are spellcasting.
Must there be some X factor to make this make sense to our human senses? Sure, but that can be a factor of a Non-euclidean, magical world, which we do not exist within.
