Bazarr
Bazarr is a companion application to Sonarr and Radarr
...Once you configure the languages and quality rules for your media library, Bazarr continuously monitors new episodes or releases indexed by those applications and automatically finds and fetches matching subtitle files, including external upgrades when better options appear. It offers both automatic and manual search capabilities through a modern web interface, letting you fine-tune what gets downloaded and stored alongside your video files. Bazarr supports a wide array of subtitle providers around the world and can track download history, manage multiple languages, and perform post-download cleanup if needed. Because it doesn’t itself scan your disk libraries but instead relies on Sonarr or Radarr indexing, it fits cleanly into automated media stacks on NAS, servers.