The voice lines are a bunch of WAV files named a certain way for actions that occur in-game. To mod them, replace each WAV file with the exact same length and same format (generally: mono, 32-bit, 11025 Hz) as the WAV being replaced. Watch this "Bug-free sounds tutorial" video by Doktor Haus to learn the steps to change survivor voice files.

The survivor voice lines are located in sub-folders (listed below) of the main L4D2 folder that is by default located here:

C:\Program Files (x86)\Steam\steamapps\common\left 4 dead 2\

Note that there are thousands of files for each survivor.

• • Bill

    • 1,214 files: left4dead2_dlc2\sound\player\survivor\voice\namvet

    • 925 files: left4dead2_dlc3\sound\player\survivor\voice\namvet

  • Coach

    • 2,420 files: left4dead2\sound\player\survivor\voice\coach

    • 313 files: left4dead2_dlc1\sound\player\survivor\voice\coach

  • Ellis

    • 2,616 files: left4dead2\sound\player\survivor\voice\mechanic

    • 463 files: left4dead2_dlc1\sound\player\survivor\voice\mechanic

  • Francis

    • 206 files: left4dead2_dlc1\sound\player\survivor\voice\biker

    • 1,636 files: left4dead2_dlc2\sound\player\survivor\voice\biker

    • 1,240 files: left4dead2_dlc3\sound\player\survivor\voice\biker

  • Louis

• • 1. 138 files: left4dead2_dlc1\sound\player\survivor\voice\manager

    2. 1,318 files: left4dead2_dlc2\sound\player\survivor\voice\manager

    3. 976 files: left4dead2_dlc3\sound\player\survivor\voice\manager

• • Nick

    • 2,547 files: left4dead2\sound\player\survivor\voice\gambler

    • 421 files: left4dead2_dlc1\sound\player\survivor\voice\gambler

  • Rochelle

    • 2,090 files: left4dead2\sound\player\survivor\voice\producer

    • 450 files: left4dead2_dlc1\sound\player\survivor\voice\producer

  • Zoey

    • 155 files: left4dead2_dlc1\sound\player\survivor\voice\teengirl

    • 1,683 files: left4dead2_dlc2\sound\player\survivor\voice\teengirl

    • 1,292 files: left4dead2_dlc3\sound\player\survivor\voice\teengirl