Place either of the "Sven's English subtitles" folders into your "steamapps\common\Team Fortress 2\tf\custom" directory.
Enable closed captions (or subtitles) in the "Audio" tab of Team Fortress 2, and play. If you find any spelling errors or missing captions, let me know.
To uninstall: Delete the folders. Pretty easy stuff.
Addendum: I know that these aren't in VPK format. I have tried putting them into the VPK format but, for some reason or another, the game doesn't load the addon correctly when they are. However, and this is the important part, the subtitles will work on literally every server (at least unless the server owner is so paranoid that they block EVERY custom file), including highlander or (in my limited experience) tournament servers. Please note that this mod only covers character dialog within a certain distance, and does not include weapon sounds (so everyone who thinks that it's "cheating" because you can hear a Spy decloaking, it's not because you can't).