“Decimating” no longer means killing ten percent as the Romans did; now it is used to mean the killing of a majority, so it’s close to the opposite of its original meaning.

We were always supposed to put punctuation inside quotation marks; however, now it seems to be the user's choice of inside or outside. And I have to admit that most of the time when I’m using quotes, it seems more logical to me to place the punctuation outside of them.

Loose and lose might as well be the same word these days. Drives me up a damn wall.

That and "POV" doesn't mean what it used to mean anymore. Also drives me up a wall.

Australian English language is now largely Americanised, a process that started in the post-war era is now mostly complete.

• Terms such as 'gaol' have been widely replaced by 'jail'.
• 'Programme' is mostly replaced by 'program'.
• A 'car bonnet' is likely to be called a 'hood'.
• 'Play lunch' is mostly replaced with 'recess'.
• 'Pusher' is mostly called a 'pram'
• 'Lacker band' is now mostly just 'rubber band'.
• 'Boomer' no longer means kangaroo, but instead 'Old person.'

I'm not really bothered by it or anything, but it's been interesting to see it shift even over my lifetime.

Literally is still understood, it just gets misused.

Going in a bit of a different direction, emojis and things like /s are well understood now, which is an addition.

"begging the question". it's not the same as "bringing up a question", it means assuming your conclusion is true in the course of an argument

I suppose the word "boomer" has changed meaning very quickly. It rarely gets used anymore to refer to actual boomers (people born just after WW2) and instead now can refer either vaguely to anyone older than 30, or anyone with an antiquated/problematic notion of social norms.

I miss double spaces after periods.

From my perspective, literally being used for emphasis does not actually change its meaning, it’s simply hyperbole.

If you complain that you’ve been “waiting for hours”, even though it’s been 45 minutes, that doesn’t change the meaning of “hours”, you’re just exaggerating.

Hyperbole is a stylistic element; style is a completely different level of language than grammar/spelling/semantics (word meanings). As another example of style, ending a sentence with a preposition is grammatically correct but stylistically not recommended.

Presently used to mean "soon" or "in a bit" but now means "happening right now"

The meaning of bemused is similar to "befuddled", but it's more often used as if it means "amused"

It used to be a firm rule that you mustn't end a sentence in a proposition.

While not totally gone, German's genitive case (which is used to show ownership) is becoming less and less common. They have both the genetive case as well as their equivalent of " 's " - which is just "s," if you're wondering. Example:

Der Herr der Ringe.

The Lord of the Rings. It would normally be "die Ringe," but it becomes "der" in the genetive case.

Another transition in German is that the "formal you" is being used less and less frequently. I understand this is the case for a few other European languages as well.

Pour one out for the Oxford Comma .

Let's eat Grandma

Commas save lives!

also i fear that "comfort" is losing the battle to "comfortability"

People no longer double-space after sentences.  No one cares that further compares metaphorical distance and farther compares physical distance.  Most people seem to think that joining two independent clauses with a comma (a comma splice) is just fine.  Things are now done on accident instead of by accident.  Compute used to be something you did; now, it's something you rent.  People seem to have given up on less being used for uncountable things and fewer for countable things.  Now they just use less for everything.  People these days are enamored 'by' something instead of with it (or of it, for our British friends).

People using then instead of than. I never saw that 30 years ago.

Ain't ain't a word.

It is now.

“Casted”

The past-tense of cast is cast. “The fisherman cast their line into the river.” “The actor was cast in the leading role.”

Casted makes you sound like a child.

would of literally their

Not exactly what you're asking, but double spaces after ends of sentences.

Ending sentences with propositions, and getting them jumbled around. My work does it in their advertisements and i cry every time.

"See what classes you can register for." Or modifying it to be worse; "see what classes you can register for fast"