Exegesis:

kai pothen moi touto hina… ‘and whence (comes) this to me that…’ pothen ‘whence,’ sometimes used to indicate surprise at the cause or reason of something: ‘how is it possible that…,’ cf. Mk. 12.37. moi is best taken as an ethical dative with little or no emphasis. touto refers to the subsequent clause introduced by hina. hina originally an indication of purpose, often denotes content in the New Testament, cf. Moule 145f.

elthē ‘comes’ or ‘has come’; the subjunctive, obligatory after hina has lost its modal function since hina has ceased to indicate purpose.

hē mētēr tou kuriou mou ‘the mother of my Lord’ i.e. the mother of the Messiah, cf. on v. 6 sub (3).

pros eme ‘to me,’ emphatic.

Translation:

Why is this granted me, or, ‘how is it that it should be done to me’ (Ekari), “Who am I” (An American Translation, New English Bible), “why should this great thing happen to me” (Good News Translation), ‘whence (or, who gave me) this good fortune’ (Javanese, Sranan Tongo), ‘whence is this honour to me?’ (Marathi, where the clause has to be in final position). Elsewhere the rhetorical question may have to become a statement, introduced by some phrase like, ‘it is astonishing that,’ ‘I can’t believe that.’

Lord, see on v. 6, sub (b).

Should come to me, or, making explicit the speaker’s humble mood, ‘is so kind to come to me’ (Apache, Balinese), cf. also, ‘would fain visit one such as this one here that I am’ (Tboli, the circumlocutionary rendering of the object bringing out the emphatic force of the pronoun). For the verb cf. also v. 28.

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.