Exegesis:

eisēlthen de Satanas eis Ioudan ‘then Satan entered into Judas,’ ‘took possession of J.,’ elsewhere in the sense of demon possession (cf. on 8.30), but here in a somewhat weaker sense, since Judas does not henceforth appear as a demoniac who is not acting of his own will.

ton kaloumenon Iskariōtēn ‘called Iscariot,’ cf. on 6.16.

onta ek tou arithmou tōn dōdeka ‘belonging to the number of the twelve.’ tou arithmou may be taken as semantically redundant, or as meaning ‘group,’ preferably the former. For hoi dōdeka cf. on 8.1.

Translation:

Satan entered into Judas. A term for demon possession (cf. on “had … demon” in 4.33) is often also acceptable in this context, but if one has the choice between a technical term and a less specific one, the latter is to be preferred, cf. e.g. ‘come upon,’ as against ‘jump upon’ in 8.30 (Sranan Tongo). Elsewhere a term referring to an emotional seizure or a bad influence is used, e.g. in Shona 1966, where the verb ‘to enter’ can have this figurative meaning. In Tzeltal the rendering is built on an idiomatic phrase, ‘he has the devil in his heart,’ which is used both for demon possession and for badness. For Satan see on 10.18.

Called Iscariot, or, since the reference is not to Judas’ proper name but to an additional name, “surnamed I.” (The Four Gospels – a New Translation, similarly Bible de Jérusalem, Toraja-Sa’dan), ‘named also I.’ (Balinese).

Who was of the number of the twelve, preferably, “one of the Twelve” (New English Bible), cf. on 8.1.

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.