Exegesis:

kai exaiphnēs egeneto sun tō aggelō ‘and suddenly (or, ‘unexpectedly’) there was with the angel…’; egeneto is used here as a substitute for a form of eimi ‘to be,’ exaiphnēs also 9.39.

plēthos stratias ouraniou ‘a great company of the heavenly army’; the genitive refers to content (to be interpreted as ‘consisting of’).

stratia ouranios (both words †) ‘heavenly army,’ scil. of angels, cf. 1 Kings 22.19.

ainountōn ton theon kai legontōn ‘praising God and saying’; both participles are appositive to the preceding stratias ouraniou but are in the plural as if aggelōn preceded. legontōn ‘saying’ serves to introduce the content of the praise.

Translation:

There was with the angel …, or, ‘suddenly there-appeared/became-visible near the angel’ (Bahasa Indonesia KB, similarly Ekari), ‘there joined themselves to the angel…’ (Bible de Jérusalem, similarly Tagalog), ‘the angel was surrounded by…’ (Vai), ‘there came to the side of the angel…’ (Sranan Tongo).

A multitude of the heavenly host, or, ‘a numerous heavenly army’ (Sundanese), ‘many heavenly soldiers’ (Batak Toba). For multitude cf. on 3.7, for heavenly on “heaven” in v. 15. Since in host the emphasis is not on the military aspect, “heavenly host” may also be rendered by ‘those from heaven’ (Tboli), ‘inhabitants of heaven’ (Thai).

Praising God and saying. In some receptor languages words of praise are preferably not introduced by ‘to say’; hence, ‘they praised…, thus their praise’ (Balinese, Sundanese), “praising God and singing” (The Four Gospels – a New Translation). To praise is often rendered by a descriptive expression, e.g. ‘make-great, or, make-great the name of’ (Tae,’ in v. 20), ‘to speak well of’ (Western Highland Purepecha), ‘lift up the name of’ (San Blas Kuna, Kpelle), ‘to sing the name of’ (Huehuetla Tepehua), ‘to make good’ (Highland Totonac), ‘to say good about’ (Tzeltal), ‘to make known something good about’ (Navajo).

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.