If you really want to have all 8 survivors in all campaigns for all game modes. I recommend using these Sourcemod and Metamod plugins and extensions.

(L4D2) All 8 Survivors For Windows (20/9/2018)[forums.alliedmods.net]

This is much better and will avoid fewer mistakes. Instead of using the Admin System because it is simple and less limited to spawn all 8 survivors together.

and if I don't have a server, but I need an addon for the locale, too, or what?

engine error 3/ - player: util_setmodel not precached models/survivors/survivor_manager.mdl

Αναρτήθηκε αρχικά από Хината Hyuuga:

and if I don't have a server, but I need an addon for the locale, too, or what?

It works for local server too. In case you don't have a dedicated server.

Αναρτήθηκε αρχικά από Хината Hyuuga:

engine error 3/ - player: util_setmodel not precached models/survivors/survivor_manager.mdl

I don't know what error happened here. But there you have the installation of Sourcemod and Metamod step by step, then the same in the link that happens to you and look at the description to install the new versions.

If not, the other one you have left is this. If you know how to create vpk files then you know what I show you:

1. Go to the location: Steam\steamapps\common\Left 4 Dead 2\update and find the file pak01_dir. Open it (you will need the GCFScape to open and extract vpk files)
   
2. You extract the folder "missions" with all the files together (minus the credits) in a new folder that you create and name any.
   
3. In each campaign file from 1 to 14, you will only modify the files: 7, 8, 9, 10, 11, 12 and 14 which are the campaigns with the l4d1 survivors.
   
4. There where it says "survivor_set" "1" you change it to value "2" to port l4d2 survivors to l4d1 campaigns.
   
5. Once this is done, you take the modified folder to the vpk application to convert it into vpk format and take it to the addons folder. Check out a guide on how to create vpk files.
   
6. And voila, you have all the official campaigns with the l4d2 survivors. There you can use the Admin System command to add to the L4D1.

Note: This may give a small bug where the cutscene intro for l4d2 survivors won't be displayed on l4d1 maps, but it's not much of a problem.

Any questions, consult the guides or forums on how to create vpk files and how to take them to the addons. Or how to extract with the program that I told you before. Good luck!

And how to do it, I just don't know, and so on.
if who knows, can someone throw it off?
I just want to remove this error
"Please"

I found these 3 mods that I hope you find useful. Try them one by one to see that everything works out for you. The latter requires having Sourcemod and Metamod installed.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1903181405&searchtext=l4d2+survivors+on+l4d1+campaings
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1221168580&searchtext=l4d2+survivors+on+l4d1+campaings
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2284474008&searchtext=l4d2+survivors+on+l4d1+campaings