Why are my subtitles showing weird characters?
Subtitles showing weird characters have one of three causes, and what you see tells you which. Letters swapped for odd pairs such as é or пр mean the file is being read in the wrong encoding. Empty boxes mean the player's font has no shapes for that alphabet. Question marks mean the letters were lost when the file was saved, and can't be recovered.
Odd letter pairs: the encoding
Older subtitle files, especially Arabic, Russian, Greek, Turkish, Korean and Chinese ones, were often saved in a regional encoding such as Windows-1256 or EUC-KR. Modern players assume UTF-8 and show nonsense. Fix subtitle encoding detects the original encoding, shows you a preview, and saves the file again as UTF-8, which every player reads.
Empty boxes: the font
The text is fine, but the player is drawing it with a font that lacks those characters. In VLC, open Tools, then Preferences, then Subtitles / OSD, and pick a font that covers the alphabet, such as one from the Noto family. Arabic and Chinese are the usual cases.
Question marks: lost letters
Somewhere along the way the file was saved in an encoding that couldn't hold those letters, and they were replaced. No setting brings them back. Find another copy of the subtitles, or transcribe the video to make new ones.
Questions
Why do Arabic subtitles show weird symbols in VLC?
Almost always the encoding. Arabic SRT files are often Windows-1256. Re-save as UTF-8 with Fix subtitle encoding, or set VLC's default subtitle encoding to Arabic.
Why does my TV show the subtitles wrong when my computer doesn't?
TVs are stricter about encoding. A UTF-8 file usually works, though some older Korean TVs want EUC-KR SMI files: Convert to SMI saves those.
Will converting the format fix it?
Only if the conversion also re-saves the text as UTF-8. Every file this site saves is UTF-8, unless you choose EUC-KR.