If all you are seeing is gibberish characters as subtitles in VLC, you are probably using the wrong encoding. For example this is what I get when I load a Bulgarian subtitle:

Here is how to solve this problem:

Tools / preferences / subtitles & OCD / default encoding

from there change the encoding to match the subtitle language, in my case I have to change it to Cyrillic, since Bulgarian alphabet consists of Cyrillic characters.

For Western European languages UTF-8 encoding is fine

You will need to reload the subtitles for changes to take effect.