Anyone who plays the game in 1440p or 4K will notice that the subtitles as well as other texts such as the loading screen tips are very small if you don't have a huge screen.

To fix it go to Documents\My Games\UnrealEngine3\MonkeyGame\Config and open MonkeyEngine.ini

Look for SubtitleFontName=MonkeyFonts.BasicFont and change it to SubtitleFontName=EngineFonts.LargeFont

Save and you're done, but make sure to change the file to 'Read-only' or the game might override your change.