Reference for Megillah 2:1
הַקּוֹרֵא אֶת הַמְּגִלָּה לְמַפְרֵעַ, לֹא יָצָא. קְרָאָהּ עַל פֶּה, קְרָאָהּ תַּרְגּוּם, בְּכָל לָשׁוֹן, לֹא יָצָא. אֲבָל קוֹרִין אוֹתָהּ לַלּוֹעֲזוֹת בְּלַעַז. וְהַלּוֹעֵז שֶׁשָּׁמַע אַשּׁוּרִית, יָצָא:
If one reads the Megillah in inverted order he does not fulfill his obligation, it being written (Esther 9:28): "And these days are commemorated and celebrated." Just as celebration cannot be inverted (it being impossible for the fifteenth to precede the fourteenth), so commemoration (the reading of the Megillah) cannot be inverted.] If he reads it by heart, or in Targum, or in any language, he does not fulfill his obligation. [("by heart":), it being written here "commemorated," and, elsewhere (in respect to the eradication of Amalek - Exodus 17:14): "Write this as a commemoration in a book." ("or in Targum, etc.":) This is what is meant: If a Hebrew reads it in Targum, and he does not understand it; or if he reads it in any other language that he does not understand, he does not fulfill his obligation.] But it may be read to those speaking a foreign tongue in their tongue, [so long as it be written in that tongue, so that he not read it by heart.] And if one speaking a foreign tongue hears it in Ashurith, he fulfils his obligation. [Greek is like Ashurith relative to this halachah. It is just that the original Greek has been lost and been forgotten as we wrote above (1:8)].