What irritates you the most with your own language?
Mine is people who separate words when they write. I'm Norwegian, and we can string together words indefinetly to make a new word. The never ending word may not make any sense, but it is gramatically correct
Still, people write words the wrong way by separating them.
Examples:
"Ananas ringer" means "the pineapple is calling" when written the wrong way. The correct way is "ananasringer" and it means "pineapple rings" (from a tin).
"Prinsesse pult i vinkel" means "a princess fucked at an angle". The correct way to write it is "prinsessepult i vinkel", and it means "an angeled princess desk" (a desk for children, obviously)
"Koke bøker" means "to cook books". The correct way is "kokebøker" and means "cookbooks"
So in German we have these weird symbols: äßöü one of them is even in my name.
In my opinion they are not necessary and cause more trouble that they are worth.
UTF 8 has alleviated some of the pain. However I still regularly find documents encoded in old character encodings and I have to manually fix all these accents.
I also have one of them in my name. In the past in school a SYS-Admin entered my name with an ö instead of the alternate form oe. All was fine. I was about 13yo, so I had no idea about backups and didn't care.
I stored all my files on their NAS. One day they had drive failures and could recover all data except from students with accents in their name. I don't know what shitty software they used but I am still annoyed at this.
We also have das,dass which I always get wrong while writing texts.
There are some good things.
The time forms can be pretty fun to use.
All in all German is a 6/10 for me could be better could be worse.