The other day on a blog I read often, I left a comment in German. After posting it I re-read it, and noticed a rather obvious grammatical error (ein ungehuerlich Grammatikfehler). I left another comment in German to point out this error, and to rewrite the paragraph that had contained den ungehuerlich Grammatikfehler.
Another commenter, a native German-speaker, on reading my amending comment, left a comment pointing out that my amending comment had more Grammatikfehler than the Grammatikfehler I had corrected. I have no reason to doubt this commenter.
I began teaching myself German about fourteen years ago from a book called "German Made Simple". After going through all the chapters, and doing all the exercises over a few weeks, I started going to the websites of German newspapers and magazines to read in German what was going on in Germany and in the world. I have been doing this ever since.
But, the fact is that, after regularly reading the news in German for going on fourteen years, I still can't write German without the aid of Google Translate and the various other online German-language resources on the Internet. Even then, the German I produce is still filled with Grammatikfehler.
Fourteen years ago, in my naivety I thought I just had to read regularly in German, and, after a few years I would consequently be able to write elegant and faultless German. But, it would seem that one has also to learn to speak a language as well as reading it, to be able to write that language elegantly and faultlessly.
Four years ago I began on French in the same self-taught way as I had done with German. While I can now read the news in French with a reasonable degree of comprehension, I can neither write it without the aid of Google Translate and the other online French language resources, nor can I speak it.
I have long thought that native English-speakers whose written English is terrible, and their spelling terrible too, should merely read, read, read, read, and read, and always do this. But the reading should be of well-written stuff, not of trash. If you are such a native English-speaker and you do as I say, you'll soon find yourself using words you'd never before thought of. You'll also write a lot better and spell a lot better.
Of course you'll only be able to do this because you're also speaking English every day, since it's your native tongue.
What's the next language I'll begin on? Spanish I think.