An "undub" is a fan-modified ROM where the localized English voice files are replaced with the original Japanese audio files.
Let’s say you own a physical copy of Rune Factory 4 for 3DS, and you want to create your own UNDUB version for personal backup and emulation. This is legally permitted in some jurisdictions as a “format shift” or “archival copy” (though check your local laws). Rune Factory 4 -Decrypted- 3DS -UNDUB- ROM -Reg...
As the progress bar crept forward, Kaito thought about the "Reg" at the end of the filename. It wasn't just a region tag; it was a signature of the last person to compile this version before they disappeared from the forums. An "undub" is a fan-modified ROM where the