Exegesis:

ho de epitimēsas autois parēggeilen lit. ‘but he charging them, ordered’ i.e. “he gave them strict orders” (New English Bible).

mēdeni legein touto ‘to tell nobody this.’ touto refers to Jesus being the Messiah.

Translation:

He charged and commanded them to tell this to no one is more emphatic than the expression used in 5.14 (which see), because of the use of two verbs, the one reinforcing the other, and often rendered by one verb or phrase such as, ‘he commanded them strictly (or, on a severe tone) not to…’ (cf. Translator’s New Testament, Bible de Jérusalem), ‘he forbade them emphatically/strongly to…’ (cf. Willibrord, Bahasa Indonesia 1968), ‘they were admonished, not allowed to spread-the-news to whomsoever’ (Balinese); Javanese shifts to direct discourse with a strong prohibitive form in it, thus, ‘he told the companions, “Do not at-all speak about this matter to anyone” .’

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.