If you know how to mod an Unreal Engine game, it should be pretty simple for this one.

The tools:
https://github.com/4sval/FModel (Standard viewing of the files inside the PAK, and y'know... extracting them)
https://github.com/klimaleksus/UE4-locres-Online-Editor (Editing them funny letters to your heart's content)
https://github.com/atenfyr/UAssetGUI (So you can read the uassets and edit them)
https://github.com/trumank/repak (To repackage them unPAK'd files)

Once you're actually ready to REPAK, make sure to add the "--version V4" context in the cmd, so you'll convert it to a readable PAK for OTWD.
For an example: repak pack --version V4 "COOL MOD FOLDER"