Exegesis:

pasa pharagx ‘every valley, or, ravine.’ pharagx in Is. 40.4 and elsewhere renders Hebrew gaiʾ ‘valley.’ This rendering also here.

plērōthēsetai ‘shall be filled.’ The future tenses of v. 5 may be interpreted as imperatives (continuation of v. 4) or as referring to future events, as v. 6. The later is preferable. For pleroō cf. on 1.20; here it is used in a literal meaning.

pan oros kai bounos tapeinōthēsetai ‘every mountain and hill shall be levelled.’

bounos (also 23.30) ‘hill.’

tapeinoō here ‘to level,’ elsewhere ‘to humble.’

kai estai ta skolia eis eutheian ‘the crooked (places) shall become a straight (way).’ The future tense has the same meaning as that in the preceding clauses, see above.

skolios ‘bent,’ ‘curved,’ ‘crooked.’ ta skolia, as the gender shows, does not refer to existing roads but to places that were too crooked to have any roads at all.

eutheian scil. hodon ‘a straight road.’ Other manuscripts read eutheias, scil. hodous ‘straight roads,’ cf. Nestle.

hai tracheiai eis hodous leias ‘the rough ways (shall become) smooth.’ From the preceding clause a form of the verb eimi ‘to be’ has to be supplied, i.e. esontai. Here the reference is clearly to existing roads that shall be made smooth.

trachus ‘rough,’ ‘uneven.’

leios ‘smooth.’

Translation:

Where a passive construction cannot be used one may employ such a rendering as ‘every valley shall fill-up, every mountain … shall go-down. Roads that are crooked shall straighten-out, roads that are bumpy (lit. holes-holes) will be measure (=level) ones’ (Kituba), or (in lines c, d) ‘the crooked paths shall become straight, the bad paths shall become pleasant to walk’ (Sranan Tongo), or, with an explicit reference to the agent, ‘God will fill … bring low…’ etc.

Be filled, or a more specific term, ‘be earthed-up/filled up’ (Javanese, Balinese).

Mountain and hill, or, where such a pair of close synonyms does not exist, ‘mountain and little-mountain’ (Kituba), ‘hill and rise in land’ (Kele), ‘mountains high or low,’ ‘hills big or small.’ Hindi can use the feminine form of ‘mountain’ to refer to a hill.

Brought low, or, ‘caused to be low,’ “levelled” (New English Bible, An American Translation, similarly in Javanese, Tae’).

One, or both, of the contrastive pairs crooked – straight, rough – smooth may have to be rendered by a negative-positive phrase, e.g. ‘the not-straight shall be made straight’ and/or ‘the not-smooth shall be smoothed’ (the latter in Toraja-Sa’dan).

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.