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First of all, I just want to translate Friday the 13th: The Game but i didn't know anything about tools or codes. Can anyone help me about what tool i need to use?

This game is on Unreal Engine 4 so you need to use quickbms script probably
https://zenhax.com/viewtopic.php?f=9&t= ... 251#p56251
to unpack content and then some locres tools to modify language files
https://zenhax.com/viewtopic.php?t=1022

When i try to unpack the .pak file, it's asking me for a variable KEY. What should I do?

In this situation you should type a valid key for the game to unpack content.
There are sites on the internet where you can find collections of such keys.

I have grabbed one for you:

Thanks to you, I'm in localization file. But there is one problem too, in localization file there is a Game.locmeta file. I was expecting .locres file, what should I do again?

I don't know, upload some samples to analyze and we'll see

Edit: I have searched the web and found this

LocMeta (Localization MetaData Resource) and LocRes (Localization Resource)

Are you sure you looking for text properly?
Maybe try total commander method first https://ikskoks.pl/searching-text-strin ... commander/

https://resmim.net/i/smJR

as you can see, there is just a .locmeta files.

No, it's definitely wrong file. It has 1KB of total size. Language files are often much larger.
Use my total commander method to search for text or just look for files in other folders.