Exegesis:

egō gar dōsō humin stoma kai sophian lit. ‘for I will give you a mouth and wisdom.’ egō is very emphatic. stoma is used in a figurative sense, and it may either refer to power of speech (Plummer) or eloquence, or go with sophian as a hendiadys and mean ‘words of wisdom.’ The latter appears to be preferable.

hē ou dunēsontai antistēnai ē anteipein ‘which cannot resist or contradict….’ hē (dative) refers, strictly speaking, to sophian alone, but is to be understood as taking up the one concept of stoma kai sophian.

anthistamai ‘to resist,’ ‘to withstand,’ here referring to resisting the power or strength of their speaking.

anteipon ‘to speak against,’ ‘to contradict,’ here used in the sense of arguing against the defence of the disciples.

hapantes hoi antikeimenoi humin ‘all your opponents,’ cf. on 13.17.

Translation:

For I will, or to bring out the emphasis, ‘for it is I who will.’

Give you a mouth and wisdom, or, following the interpretation preferred in Exegesis, ‘give you words of wisdom (or, words which are wise),’ ‘cause/help you to speak wise words, or, wisely.’ For wisdom see on 2.40.

Which none … will be able to withstand or contradict has resultative force, ‘so that no one … will be able to withstand or contradict them, or, such words.’ If in the receptor language one or both verbs require a personal object, one may say e.g. ‘resist you and refute such words,’ or, ‘resist and oppose you (when you speak so).’ — To withstand. In Sranan Tongo the idiom is here, ‘to put to one side.’ — To contradict, i.e. to oppose (a person) in argument, or, to deny the truth (of something that is said).

Adversaries, or, ‘opponents/enemies/accusers.’

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.