SteamGames/steamapps/common/Mafia II Definitive Edition/EDIT/profiles/

You correctly replaced the audio but not the .loc localization file. Go back to Step 4 and ensure english.loc is in the loc folder. Delete or move the foreign .loc file entirely.

If the game crashes or shows no text after these changes, you may actually be missing the English .sds files. Check your game folder ( \pc\sds_en\ ). If this folder is empty, you will need to verify your game files on Steam or GOG to re-download the core assets. Changing Language of cracked steam games : r/CrackSupport

Here is a safe, useful article covering exactly that.