If you make another game (just not "PlaneShift") with the sourcecode, you can make your own world and races too. Then you will also need your own gameserver (and it will not be a "PlaneShift" game server, but a "your game" server).

Although the "source code" is OpenSource, the whole game "PlaneShift" content is licensed, and its content has to be approved by Luca "Talad" Pancallo. You cannot add anything to "PlaneShift" as you like -- then it would not be "PlaneShift" anymore.

You may change the source code to make your own game out of it, if required. But you should publish the changes to the public domain too. And those changes may probably not enhance "PlaneShift", but possibly only "your game"... If you want to contribute to "PlaneSHift" specifically, you must be part of the team, and cooperate with the hierarchy of the existing development team.

what to do to join the team?
What knowledge is necessary to have?
and if I do it for discussion with the creators of the game at the expense of creating addon
it is possible that they would agree?

I never understood
if I'll create a site in Russian then I will need to make separate Russian server?
or both players will be registered with the Russian site?
and it will be fun game site or  rank official Russian site of game?

Why?
and when I downloaded open source code and make their game it is possible?

Welcome to the PlaneShift forum.

You want to create a website about PlaneShift in russian? ... In general, I believe, you may do so. Write about news. Maybe offer a place for an own community (a forum or similar). Like the german community does - http://www.psde.de

The source code, though, is provided via SVN on SourceForge. That should be the only valid place to get the source from - because only there it is both up-to-date and moderated (and therefore safe from unauthorized changes). The PlaneShift Build Guide explains in detail how to do it for different operating systems.

If you need direct help in russian, I am quite certain that someone in our IRC channels can help you "live".

irc://chat.eu.freenode.net | http://webchat.freenode.net -- channels: #planeshift (generic talk) | #planeshift-build (about sourcecode and building)

OK!
Then next week I'll start doing the site in Russian!
With regard to source code, try to ask friends who know English, download