it's working now, i don't know what i did but works great.
Thanks you anyway for reply and helping me to solve it.

first thing i solved by adding this code into com_sef/models/config.php (about 217 line) -

It's who wants your default template 404 error to be shown.

Still waiting for reply about second thing.

Hello,

I wanna ask about 404 error page. There is some way to change it to template default 404 page?
And another- about overrides, i have joomla default contact form, when i change constants text and switch to other language, happens nothing, it doesn't want to translate and russian word stays. (My primary language is Russian on website)
But when i change in core language files, it's translating.
Some suggestions?