And by "stillborn", I mean a dead language that never really lived to begin with: a modernized version of an archaic language frozen in time, or an all-out archaic language (with archaic grammar and vocabulary), but with modernized pronunciations (and all the vowel shifts and consonant shifts applied). Like Classical Latin, which was probably never spoken in daily life (in contrast with Vulgar Latin).
Or just simply a language that is based off an actual natural language, but highly stylized and artificial, having had diglossia with its parent-language since the start, never having been an actual spoken language at any point in history.