In addition to Subscene, D-addicts also has a lot of subtitles and concentrates more on Korean TV dramas. Since you mention seasons, I assume your "movies" are actually TV series.
If the subtitles are in .srt format, most players will automatically add them if you give them the same filename as the movie and put them in the same folder. The time indexing may be slightly off though (usually time-shifted forward or back). The better players have settings to let you time-shift the subtitles. The bigger problem is when the movie's framerate has been altered, usually from 29.97 fps (standard for movies converted to video), to 30 fps (standard for computer video). This will cause the subtitles to start synchronized with the move, but slowly drift apart as the movie progresses.
If your player doesn't let you time-shift the subtitles, Subtitle Edit will let you re-index the subtitle file. I think it'll also let you scale the time index, which can take care of the 29.97 vs 30 fps problem. But it's been so long since I used it I don't remember for sure.
If you don't like the subtitle file being separate and want to combine them into the movie file, that gets a little trickier. The movie file is actually just a container, containing a video file, audio file(s), subtitle file(s), and chapter index. Some container formats can store more stuff. First you need to break apart the container in a process called demuxing (de-multiplexing). Then you recreate a container by muxing all the files together again, this time including the subtitles. I haven't done this in nearly a decade so won't recommend any software. Instead, read up on it here.