Someone asked: As the Nabi SAW has said the closest place to Allah is the sajdah so supplicate there. Is it aloud to formulate our own dua in our own language in sajdah after reciting 3 times subhana rabbiyal ala? And is it aloud to do this in every prayer (farz,sunnah,nafil)?
Answer: The Prophet did not say "closest place", but something like "The closest one is". This has nothing to with place, because Allah is the Creator of place and is therefore not in a place or direction. Closeness here has the meaning of acceptance, not place. It is blashemy to believe that Allah is in a place, because being in a place is an attribute that must have a beginning, since place itself has a beginning. Anything with a beginning needs a creator, and Allah does not need anything. If someone believed that Allah is in a place, he needs to become muslim by saying the shahaadatayn, intending to become muslim and leaving what contradicts the islamic belief.
You should not formulate your own duaa in other than Arabic if you are able to speak Arabic. You should also not go beyond "subhaana Rabbiya-l-'a^laa" in fard prayers, but you can say this phrase as many times as you like for a total count that is an odd number, such as 3, 5, 7, etc. Three times is the minumum sunnah. In other prayers you can add other phrases, but make sure that you make duaas that have been related or are similar to those related. If you ask in a way that sounds like ordinary speech it will invalidate the prayer. The best and safest is to make Arabic duaas that have been narrated in hadith.
... and Allah knows best.