If you wanted to manipulate YouTube to return strictly Serbian results then you should start searching and viewing exclusively Serbian videos. I suspect there will be no shortage of interesting content.
Unfortunately Serbian videos aren’t automatically subtitled by YouTube even though transcription error rates for the language are quite low.
Due to LingQ’s policy of not transcribing YouTube audio you would need to find the YouTube video and download the audio and create a new lesson with it.
LingQ has an official solution for this (but its not a great one)
You can import and transcribe directly into LingQ from Youtube with Rooster Video Tools although that is a paid solution.
For content outside YouTube.
A quick search for Serbian content revealed this website.
Radio/Movies/Series/Education - I think you could find most things…
A few things to mention:
- Requires an inexpensive sub.
- All content is under DRM and cannot be played if downloaded
- No content is subtitled
With these restrictions this is what I would do
- Screen Record the content as it plays (including the audio)
- Convert the file to MP3 and upload to LingQ as a new lesson using the web UI.
- If LingQ transcription fails or is subpar I would run the same audio through a different transcription provider and upload the subtitle file it generates to LingQ