The safe bet for games that don't say anything about subtitles on their respective GOG page is to assume they don't have any. It's important to note that most of the games on GOG are well over 10 years old now, and at the time subtitles were not considered necessary by most developers (unless of course, the game had no audio based dialogue). I certainly wouldn't expect the GOG team to modify the game beyond fixing compatability issues.
Having said that, I've always found the game audio quite easy to understand; perhaps you need better speakers or something?