@berkanteber wrote (#17 (comment)):
3.1.0 has just been approved (for Nexus and above). This should improve subtitle language identification.
The subtitle filename now (https://github.com/putdotio/putio-kodi/releases/tag/v3.1.0) has the language code/shortname appended, but it is appended after the .srt file extension. This makes "srt" part of the subtitle "name" as parsed by Kodi. In general, it also breaks filename-based file type detection
Example:
Video Name.srt - eng
English - Video Name - srt (External).