What would be a good translation of this sentence in Koine Greek?

You know, this will certainly be wrong, and too Modern Greek. But this question has been sitting here for a week, so:

Ὑψίστη ἡ τῆς σταθερότητος διαφορά. Τούτου νοουμένου, ἡ Κοινὴ τῆς ἑλληνικῆς γλώσσης διάλεκτος θέσμιος ποιεῖται. Πᾶσαι ἑτέραι γλῶσσαι οὐ στηρίξονται, ἰδίᾳ δὲ πρὸς λογίαν γραμματείαν.

Backup requested. Please do not get this tattooed without a second opinion. 🙂