Split a bilingual subtitle file into an original track and a translated track, or keep just one of them.
Handles both common layouts - one cue carrying two lines, and two cues sharing the same timeline. Tracks are split by order and script type, the timeline is kept exactly as it is, and a single-language file is flagged instead of being silently emptied.
Anyone handed a ready-made bilingual file who wants only one language, and subtitle teams who archive the original and the translation separately.