Exegesis:

kan men poiēsē karpon eis to mellon ‘and if it bears fruit for the future, …’ with aposiopesis following. kan is contraction of kai and an. eis to mellon ‘for the future,’ i.e. ‘(for) next year,’ cf. Plummer.

ei de mēge lit. ‘but if not,’ i.e. ‘otherwise,’ cf. on 5.36.

ekkopseis autēn ‘you will cut it down,’ i.e. ‘you can cut it down.’

Translation:

To bear fruit, cf. 3.8.

Next year, i.e. next (fig) season, next (fig) harvest.

Well and good, or, “so much the better” (Good News Translation), ‘then it is all right’ (Zürcher Bibel), added to complete the thought that is left incomplete in the Greek. Another solution is to change the conditional clause into a sentence in the potential or optative mood, cf. e.g. “perhaps it will bear fruit next year” (An American Translation, similarly Bible de Jérusalem, Javanese, Sundanese), or, ‘may it (or, I hope it will) bear fruit in the future’ (Batak Toba).

You can cut it down. In some languages a form showing that the subject is not the direct agent is preferable or obligatory, e.g. ‘let it be cut down’ (Shona 1966, similarly Tzeltal, Kituba, Toraja-Sa’dan), ‘you can order me to cut it down.’

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.