For English, my native language, it depends on how hard it is for me to hear what's being said. By default I don't use them, but I'll turn them on as needed. For things that are in Spanish, it depends. I'm learning Spanish, so I try to watch things in Spanish without subtitles, but if it's something that I want to make sure I understand, then I'll turn Spanish subtitles on and maybe even English subtitles if really necessary. I don't watch many things in Korean nowadays, but if I do then I'll try without subtitles first. For things in other languages, I don't speak them at all, so I'll watch with subtitles in English~