I have installed Visual Studio 2017 RC, and by default it set language to my system language (Polish) so I was trying to change it to EN but in Options > Environment > Inter
You need reinstall VS.
Language Pack Support in Visual Studio 2017 RC
Issue:
This release of Visual Studio supports only a single language pack for the user interface. You cannot install two languages for the user interface in the same instance of Visual Studio. In addition, you must select the language of Visual Studio during the initial install, and cannot change it during Modify.
Workaround:
These are known issues that will be fixed in an upcoming release. To change the language in this release, you can uninstall and reinstall Visual Studio.
Reference: https://www.visualstudio.com/en-us/news/releasenotes/vs2017-relnotes#november-16-2016