I have read that some companies like Bethesda and Valve usually accept MODS of their games on resume, I am starting a project with some friends where we are going to recreate an English server of and old Korean mmorpg and add some new features to it, would it be ok to put the game on my resume after the project is finished or it would be bad since the game still exists in Korea? (the game is free to play with cash shop, we won´t have cash shop in our server)

Private servers are usually illegal since they rely on stolen server software. So no, i don't think any company is interested in hiring people who do illegal stuff and try to brag about it.

Private servers are usually illegal since they rely on stolen server software.

Assuming that the OP's intention is to build a server compatible with the game, without reference to the original server's source code... It all ends up pretty murky, and your mileage may vary significantly from company to company.

That said, I'd highly recommend that you stick to modding a game which the publisher explicitly condones mods for, if you are intending to use it on your resume.

(as always, I am not a lawyer)

(As this is about job applications, moving to the job section of the site.)

Be careful. I'll assume that whatever you were doing is legal where you are.

If you're doing something that is potentially illegal in an area, or is illegal in other parts of the globe and was not related to professional experience or organized academic studies, it is unwise to put it out on a resume. Resume's get scattered to the wind, and they stay on the Internet forever... I can still find old editions I used in the early 1990s, before the WWW was a thing. While it may not be widely visible, thirty or forty years from now it will still exist out there. Anything you publish will be tied to your name if someone wants to spend enough time/effort/money doing the necessary digging.

Like swiftcoder, I recommend that you only talk about modding games where the publisher either designed the feature in or has been quietly supportive. Even if it was perfectly legal and done for your own learning, I would avoid mentioning modding games where the publisher has expressly forbidden modding.

The goal of a resume is to help convince the employer to bring you in to an interview. You want them to have a positive and curious attitude, leave them wanting to see more. You want to entice them, to be sexy, to impress. You don't want them to read it and feel like you're better suited for a dark alleyway or darknet development. ... unless of course it is a job doing that kind of thing.

You might discuss it during an interview, about how you've tinkered with games you own to see how they work, but I would not put that on a resume. That is personal learning, not professional/academic experience.