Perhaps you own the beautiful Space: 1999 Blu-ray box set (released by Network Distributing or Shout! Factory). These discs usually have subtitles, but sometimes only for the commentary tracks, not the episodes.
To add external Space: 1999 subtitles to your Blu-ray: space 1999 subtitles
Space: 1999 is famous for its "hard sci-fi" approach. In a single episode, you might hear references to magnetic vortices, quasars, delta waves, psycho-kinetic energy, and stellar decay. Without subtitles, catching every mutated syllable of this fictional physics can be exhausting. Subtitles allow you to pause and parse the technobabble that drives the plot. Perhaps you own the beautiful Space: 1999 Blu-ray
V or go to Subtitle > Add Subtitle File.Space: 1999 was a global phenomenon. If you are looking for localized subtitles: In VLC: Press V or go to Subtitle > Add Subtitle File