OOTP19 uses OGG files. WAV files may still work, they were used in the past. You can replace or modify the current files. You can also add files. For example there is a crowd1.ogg file, you can add a new crowd2.ogg file. When you install updates the original files get overwritten. So you must make a backup folder of any files you replaced and copy them back to the sounds folder after updating. You can use a free program, Audacity to edit or convert sound files.
https://www.audacityteam.org/