The Hebrew and Greek that is translated as «firstborn» in English is translated in a number of ways:

• «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)
• «he/she that damages the stalk (i.e. the body)» in Uab Meto (source for this and above: Reiling / Swellengrebel)
• «the oldest son of all» in Mezquital Otomi
• «oldest child» in Isthmus Zapotec (source for this and one above: Waterhouse / Parrott in Notes on Translation October 1967, p. 1ff.)
• «firstborn child, who was a boy» in Elhomwe (to make clear, without ambiguity, that Mary did not have daughters before) (source: project-specific translation notes in Paratext)

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 and firstborn.