How strictly are language rules adhered to between Pilot and ATC? My understanding is that there are general sentence structure rules that must be adhered to when there is contact between Pilot and ATC are well defined, like this.
Are these rules strictly followed in the real world, and is all other conversation fully avoided?

If not, does it happen often enough to be considered while designing an automated ATC response system? 

(Based of videos of pilots sharing lighter moments with the ATC on YouTube)
Standard Phraseology is what should be used, but especially in those countries where the local language is an allowed IFR language, you will get deviation from that in daily use, either due to dialect, accent or simply colloquial terms influencing the phraseology used between pilots and ATC.

In countries like the USA, where English is the local language anyway, you will sometimes hear non-standard phraseology being used. In countries like Germany, where English is not the local language and IFR is only allowed in English, you will have pilots and ATC adhering to standard phraseology more closely, especially to avoid misunderstanding due to local accent.



Anecdotal comment: I fly in Germany and usually use English also for VFR. Germans have a very phonetically hard sounding pronunciation in English, making the language sound clipped and sharp, which carries over to phraseology being used. Many native English speakers have commented though that this makes it really easy to understand, because every word is spoken very distinguishedly. Although I speak English fluently without accent in normal day use, I tend to slip into a German accented English in aviation... because it's easier to understand.