Several major streaming platforms provide Slovenian subtitles, though you may need to adjust your profile language settings to see them:
One unique informative feature of Lord of the Rings subtitles is the handling of Middle-earth languages (Sindarin, Quenya, etc.): complete-elvish-lotr-subtitles/README.md at main - GitHub The Lord of the Rings subtitles Slovenian
If you own physical copies without native subs or are using a media player like VLC, you can find community-made and professional-grade Slovenian subtitle files (.srt) on these sites: The Lord of the Rings subtitles Slovenian
