The failure is expected behavior and not a bug as you're missing a dependency. The Steam runtime fulfills the dependency, which is what it's for.
By "without Russian localization" do you mean you can't select Russian in the Steam options, or that the text doesn't show up in Russian or that you can't input in Russian?
I just forgot to set language after --reset.
How can I know what exactly Steam required from my system? I really want to run Steam with my system libs.
The most direct way is to run ldd on the Steam binaries, then find what packages contain the dependencies that aren't found.
In your case it's most likely Network Manager, as a dependency on that was recently added. There are several libnm* that you need. Note also that the runtime is a stable and tested platform. If you run without it you may experience incompatibilities as you're running in a configuration we don't test. You're welcome to do that, I just want to point out that your mileage may vary.
Closing this as the language issue is resolved.
Nothing extracted yet.
Steam suddenly stop working without STEAM_RUNTIME=1, I always get errors:
With STEAM_RUNTIME=1, Steam work, but without Russian localization.
"steam --reset" does not help.
Before this bug appeared, Steam work fine without STEAM_RUNTIME.