I don’t use the WebOS app but generally default subtitles/audio languages are set on your profile and the apps pick up those settings.
Try logging in to the web interface and going to your user profile. There is a “Playback” section where you can set your preferred languages. If this isn’t set it likely is taking the default language from your media files instead.




If you want the search to be flexible like handling things like root stemming (i.e. for matching words that are pluralized etc) you might want to put the text into an Elasticsearch database.
You might run into problems with the field length if these are long documents. A possible solution to that would be an putting each page into its own field inside of the document.
If this is for a non tech user to search, the Kibana interface should be relatively easy for anyone to use.