If you haven't had trouble with subtitles with Plex/Roku, then you're not trying. I found eight subtitles switches in less than an hour this morning (after spending 30 minutes last night trying unsuccessfully to get it to work so the gang could watch a movie.) Post your own and let's get this list to ten (or more).
1) Names - Folder name, .mv4, *.srt must be the same. *.srt next to *.mp4 but NOT in their own folder did not work
2) **Roku* Settings - Caption Mode = On
3) Plex Preferences on TV - Subtitles = Soft (recommended) is working for me
4) Video Playback Options for show on TV - Subtitle Stream = Unknown (SRT)* [one of the ways to toggle subtitles on/off]
5) * key on Roku remote while playing show [one of the ways to toggle subtitles on/off]
6) Plex Web Interface for the specific show - Subtitles = Unknown (SRT) [one of the ways to toggle subtitles on/off]
7) Plex Web Interface Settings>Server>Languages - Subtitle Mode = Always Enabled is working for me now
8) Plex Web Interface Settings>Web>Player - Subtitles = beats the hell out of me. I've got Burn Subtitles = Always and it's working
There's bound to be more software switches controlling subtitles. What have you found?