I was going out to the street from underground, when I saw an advertisingement of a theater play and I began to smile unwittingly to smile. I was going out to the street from underground, when I saw an advertisement of a theater play and I began to smile unwittingly.

I was goetting out ton the street from underground, when I saw an advertising of a theater for a play and I began unwittingly to smile. I was getting out on the street from underground, when I saw an ad for a play and began unwittingly to smile.

Cleaned this up for you. I’m assuming “underground” means some kind of subway, in which case “got out on” is a better expression. “Ad” or “advertisement” also better. Don’t need to clarify “theater play”; “play” is already specific to theater in this context.

The play was "La cena de los idiotas", —Dinner for Schmucks, in English, and is —a remake of a French movie namcalled "Le dîner de cons". The play was "La cena de los idiotas"—Dinner for Schmucks, in English—a remake of a French movie called "Le dîner de cons".

Em-dashes let you present the English translation as an aside, so you can get to your main point: that it’s a remake of a French movie.

It is very funny; I have watched this movie at least three times and I always I finish by laughing a lot. It is very funny; I have watched this movie at least three times and I always finish by laughing a lot.

It is very funny; I have watched this movie at least three times and always I finishend up laughing a lot. It is very funny; I have watched this movie at least three times and always I end up laughing a lot.

I will try to go watching this theater play. I will try to go watch this theater play.

"theater play" isn't an incorrect way of saying it, but native speakers will usually just say "play", as it's implied that these plays are performed in theaters.

I will try to go watching this theater play. I will try to go watch this play.