The Greek that is translated as “firstborn” in English is translated “he/she that opens the gown” in Batak Toba (because formerly a woman stopped wearing a gown and started using a bodice after the birth of her first child) and “he/she that damages the stalk (i.e. the body)” in Uab Meto. (Source: Reiling / Swellengrebel)
In Bawm Chin, the term can imply the existence of younger siblings, so a translation is needed that brings out the fact that Jesus is superior to all else, not just the first of a series. (Source: David Clark)
See also only begotten son / (one and) only son.