In German people tend to increase “only” (das einzige). As in, they say something is the “onliest” (das einzigste). It’s usually a good indicator of someone’s education.

In many regions it is common to do comparisons with “as” (wie). As in “My dog is bigger as yours” instead of “My dog is bigger than yours”. The most infuriating thing about this is that most people doing that mistake don’t even acknowledge that it is one. At least people who say “onliest” can be convinced that it is wrong.

Technically not an error but still annoying is to append an apostrophe and an s to a name to indicate the genitive. Like in “Anna’s food is good”. In German that should be written as “Annas Essen ist gut”. But due to many people making the same mistake (I guess also because we’re used to it from English sentences) it has been allowed to use an apostrophe. So in that case I’m just a grumpy old guy.

Less. It’s used eveywhere, although should only be used with uncountable nouns.

Less drama is prefered.

Fewer items left on the shopping list.

I know you’re asking for such errors in other languages, but I find it interesting that some of the common english errors are more frequent with native english speakers than with learners of english as a second language.

A good example of that is using “of” instead of “have”.
Should of… of what?? It makes no sense to me how someone could confuse the two.

Having learned english as a second language, I learned to read and write it before learning to speak it.
On the other hand, I’d expect native speakers to have learned spoken english before learning written english.
I think this difference changes which errors someone is likely to make.
Native speakers confuse of/have more because they heard it long before writing it.
People who learned it later are less likely to make that mistake, although they’re more likely for some others.

TL;DR: Native speakers are more likely to make mistakes that are homonyms. Of/have, your/you’re, etc.

As for the spirit of your question, I’ll go with french.

Almost every noun in french is gendered.
Objects, body parts, concepts, ideas, pretty much anything and everything is gendered.
It’s also super obvious whenever someone doesn’t use the correct gender for anything.
It’s also hard to explain to anyone.
There might be a logic behind it, but I don’t know how to summarize any of it.
I just know it, but couldn’t tell you why.

Some of those make no fucking sense either.
It has mostly nothing to do with women or men or gebder roles and identity, it just is.
“Jam” is a feminine noun, yet “butter” is masculine.
“Bread” is masculine, but a “loaf” is feminine.
The noun for each and every season are masculine nouns, but the word “season” itself is a feminine noun.
Also, a “vagina” is a masculine noun, because reasons? Weird.
Various different words for “testicles” vary between masculine and feminine.

It’s all super obvious to anyone who speaks french, but I never managed to explain it to any speaker of a non-gendered language like english without breaking their minds.