Good Lord... Tell me the script dialogue is at least as good as this grammatical masterpiece...
So here is my opinion on his grammar:
(Sorry HoneyGames, you know I love your games and you work your ass off being not a native English speaker)
The grammar in his games is not the best. But...you can 90% of the time deduct one 100% what the character is trying to say. The essence of what your choices will boil down to, is actually very clear. You can also clearly deduce the feeling the NPCs are trying to get across, along with facial expressions.
For this game, it's actually very important, as your character interactions is like no game I have ever played on this site. Your interactions with characters and how that effect other characters is simply amazing. So even though the grammar is far from perfect, it's good enough to immerse yourself fully in this game.
I have played some other games with Engrish that is basically unplayable, but I believe it comes down to bad script/writing.
"Hi, I are Peterz. You looks like hot. Let's fuck slut.....OK, I love you dick"
This game is not good in the English department, but the writing/script is good. Try imagining that you are in a country of foreigners, and everyone speaks to you in English, but it's not perfect, and with a heavy accent. That's what the game feels like for me.
TLDR; The English in this game is not perfect, but it's good enough to enjoy this masterpiece fully.