Exegesis:

kai poimenes ēsan en tē chōra tē autē ‘and there were shepherds in the same region.’

poimēn ‘shepherd’; according to rabbinic sources shepherds in Israel were despised and considered unreliable, cf. Strack-Billerbeck II, 113f.

chōra ‘district’ (as here), ‘country,’ ‘(cultivated) land’; the phrase en tē chōra tē autē is sometimes translated less emphatically, “in that region” (Revised Standard Version, cf. Williams, An American Translation) instead of ‘in the same region.’

agraulountes kai phulassontes phulakas tēs nuktos ‘staying out in the fields and keeping the night watches,’ appositive to poimenes and describing the activity of the shepherds. The accusative phulakas is the cognate accusative or accusative of content, etymologically related to the preceding main verb phulassontes ‘watching’ and thus specifying its meaning: the shepherds keep watch over their flock by means of phulakai. tēs nuktos is either genitive of time (but then usually without article), going with phulassontes phulakas ‘keeping watches at night,’ or, preferably, qualifying genitive with phulakas: ‘night watches.’

phulassō active: ‘to watch,’ ‘to protect,’ middle: ‘to guard against,’ ‘to look out for.’

phulakē ‘guarding,’ ‘watch of the night,’ ‘prison.’

Translation:

Shepherds usually can be described as ‘men who tend (or, feed/lead/care-for/watch) the sheep.’ In some cases such a rendering would lead to tautology, because the rest of the sentence comes near to a description of a shepherd’s job; then it is preferable simply to render ‘men.’ For ‘sheep’ see references on 15.4.

Out in the field, keeping watch over their flock by night. In a context like this some languages (e.g. Javanese, Ekari) render ‘to (keep) watch’ by ‘to stay with’; in others the rendering requires a second verb to express the connexion with the object, e.g. ‘to (keep) watch, staying-with/taking-care-of’ (cf. Balinese). In some cases the language renders the phrase ‘to keep watch at night’ by one verb (Tae’); elsewhere the language possesses one verb to render ‘to be/stay at night,’ ‘to pass the night.’ In the latter case the structure of the sentence may better be slightly changed, cf. ‘they were-passing-the-night in the fields, staying-with their flock’ (Javanese, Batak Toba). — Out in the field, or, ‘in the grass (i.e. open uncultivated areas)’ (Tboli), ‘in (the-)country (i.e. brushland, suitable for grazing), but in (the-)open’ (Kituba, which has to use two expressions in order to make it clear that they were not inside a house). For flock, i.e. a number of domesticated animals tended by a herdsman, some languages have a specific term, e.g. a word related to ‘gathered group’ (Kele), or ‘enclosure,’ by extension also used to indicate the animals normally kept there (Zarma). In other languages “their flock” has to be rendered by, ‘those-they-tend/feed’ (Balinese, Batak Toba), ‘the sheep they had to care for,’ ‘their sheep.’

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.