I read comments online, and in my experience the most difficult writing to parse isn't from foreign speakers who drop articles or mis-conjugate things - it's from people whose writing is just, for the lack of a better term,
bad. This is very common on places like Nextdoor or Facebook.
It's things like:
- total stream-of-consciousness gibberish that could probably be assembled into a coherent statement if the writer would re-read what they wrote and edit it
- A complete lack of punctuation, or even understanding of sentence and paragraph structure; at a glance, it looks like what I described above, but it's different because there's definitely a topic and a point they're looking to make, but they can't put the words together correctly.
- spelling so bad, that even with context, it's unclear what word they're intending to use.
- A wild misunderstanding of how to start and stop conversations online. (One recent example is me asking someone on Facebook if I could stop by to check out a garage sale, and a clarifying question about a term they used, only to get the response "ok." Note that in their post, they didn't specify an address beyond the name of the town they live in.)
You can definitely point out flaws in the way I grew up - somewhat solitary, spending a lot of time alone in my room on a computer connected to the internet - but I think that it at least taught me how to make myself understood in written form.