Sorry for the long time it took me to get back at your request.
I will use red for cases were the meaning is compromised, blue for cases were the conjugation was wrong, and green in case I want to suggest a different style.
Αυτό είναι το προσωπικό
Ιδιωτικό = private (ιδιωτικότητα = privacy)
προσωπικό (adjective) = personal; !! το προσωπικό (noun) = personnel, staff, employees
αφού θα το γράψω επίσης στα αγγλικά.
όπως means "as" when you are saying that one thing acts as another, eg τρέξε όπως ο άνεμος = run as the wind = run like the wind.
You need an object there, in this case the pronoun το, referring to το κείμενο.
Επίσης will have to come after the verb in this sentence. Style suggestion: use και
: θα το γράψω και
στα αγγλικά, it's a more natural/colloquial way of expressing "as well".
Αυτοί μιλάνε ελληνικά, γιατί είναι Έλληνες.
We wouldn't place a comma there.
Σας παρακαλώ μην παίζετε στον δρόμο.
Okay, this requires a somehow lengthy explanation.
First, how to negate an imperative: to give a negative command, you use the subjunctive ((να) <verb>
) and the particle μην: να μην παίξε
παίξεις, να μην γράψε
γράψεις, να μην παίξτε
παίξετε, να μην γράψτε
γράψετε. "Να", the subjunctive marker can optionally be dropped in the negation because the negation particle can only be followed by the subjunctive, so there's no need to mark that twice.
Secondly, you used the aorist/simple past there, which has a perfective aspect. This makes the negative command refer to an action that is not currently taking place, and in fact, it's completely hypothetical, eg "όταν σας συλλάβουν να μην μιλήσεις" = when they arrest you, don't talk.
To ask someone to stop doing something they are currently doing, you need to use the simple present which was a continuous aspect, eg "σας έχουν συλλάβει, μην μιλάτε" = you have been arrested, don't talk."
Now, there's always the chance you did meant to say "when you decide to go play outside, don't play in the street" instead of "you are currently playing in the street, so please stop playing in the street", but in any case you cannot negate a verb in the imperative, you need to use the subjunctive.