I have a question to fellow nonnative English speakers here: Do you have in impression that your English skills are fading, especially the grammar rules?
I can't recall when was the last time I used future perfect tense or inversion. I use know maybe 4 tenses and that's all. I have an impression that I am constantly using less sophisticated and simpler language.
On the other hand my vocabulary greatly improved.
It means that your English is becoming more natural. In natural conversation it is very rare to use the full range of English grammar. That is one of the hardest things to teach in the classroom - how to sound natural and use the same register as native speakers in the same situation.
Using the same register as native speakers is important in establishing rapport. It is called "accommodation."
When we accommodate others, we show them that we are listening. In fact, it is quite natural when we are engaged in a conversation to use accommodation effortlessly. If, for example, I am talking with someone from the Valley who uses like
in every sentence, I would also use it without thinking. Like, he like all guys wants to buy like a really expensive new car. This type of sentence, however, would not be found in a scholarly paper unless someone were to give an example of Valley Speak.