I see there is basic support for steam in esenthel, but it possible to add more options? Like unlocking achivments? Or checking if player bought dlc?

Steam sdk has really good doc and its not too hard to implementat what you need in the meantime.

But it seems that Greg was fine modifying EE source to add whats needed by the users

So I'll +1 on this

Sorry for stupid questions, but I'm confused. How can I acces steam SDK from Esenthel Editor? As I understand they already in Esenthel, but can't acces any functions from steam documantations. Do I need to download additional files and link to Steam SDK librieries in application Settings?

Sorry i am out untill sunday, and wont have access to my engine so ill use my memory only here, i believe you just need to link the steam library to EE, after that you can call function from there.
I did run into an issue at some point with automatically generated header from EE but i managed to go around it as described here https://www.esenthel.com/forum/showthread.php?tid=9452

Now I'm too busy to look into steam sdk, but a sensible approach would be to add functions to the engine source code and make a pull request on github to merge it with development branch.

Its true that it might be a better option, i used to not have source ( i know its free now ) but it might be a bit more investment to do it as you need to build the engine

on the project properties, you can add
include header : C:\public\steam\steam_api.h | C:\CallbacksSteam.h
the callbacksteam was for my personal header to have linked callbacks.
include libraries : C:\BeastsInBurrows\steam_api64.lib

and that's pretty much all you need to have access to the Steam API.

then its pretty easy, you just have to follow the doc to know what to add for your need.

then you can start the steam part by calling SteamAPI_Init();

RedcrowProd Thank you very much