Game links: 

https://drive.usercontent.google.com/download?id=10BaAnqeX1itu_kWtQJPIC-tgQ3ZJDB_P&export=download (full client of a private server that used to existed)

https://www.zone4extreme.com/download (Zone4 Extreme - The only remaining official server)

All file formats (sod for audios, img for UI images, mod for archiving models, textures, etc...) seems to use a charset replacement method (see here: https://hcs64.com/mboard/forum.php?showthread=52948), but no progress beyond that, I don't know if the method has changed over the years so i'll put the link of 2 game versions that's few years apart in case it does.

Ok, so for the private server one, i found a bms script that's able to decrypt the .sod files, as well as the .dat files which store various scripts (didn't try them on the Zone4 Extreme ones yet):

https://github.com/DKDave/Scripts/blob/32c45c3c5e6a18bd346882683653c205a95b6d3b/QuickBMS/PC/Zone_4_(PC)_SOD.bms

But it seems like the .mod and .img use a different kind of charset replacement, or even a different kind of encryption entirely. Below are some samples for the .mod and .img files in case anyone wants to take a crack at it without downloading/installing the full thing.

Zone4_Samples.zip

7 hours ago, PlsSendHelp said:

Ok, so for the private server one, i found a bms script that's able to decrypt the .sod files, as well as the .dat files which store various scripts (didn't try them on the Zone4 Extreme ones yet):

https://github.com/DKDave/Scripts/blob/32c45c3c5e6a18bd346882683653c205a95b6d3b/QuickBMS/PC/Zone_4_(PC)_SOD.bms

But it seems like the .mod and .img use a different kind of charset replacement, or even a different kind of encryption entirely. Below are some samples for the .mod and .img files in case anyone wants to take a crack at it without downloading/installing the full thing.

Zone4_Samples.zip 18.86 MB · 2 downloads

I remember doing the original script, having to get ask for unencrypted versions from memory and doing a comparison.  It looks like it's just a different replacement table, possibly the same for both img and mod as there's a lot of "E" characters, which is probably 0.  Other than that, you can't really guess easily.