How to set value to login form's submit via themename_form_alter I have theme_form_alter function, I want to set input submit value with it too

function ivanco_form_alter( &amp;$form, &amp;$form_state, $form_id )
{
    if (in_array( $form_id, array( 'user_login', 'user_login_block')))
    {
        $form['name']['#attributes']['placeholder'] = t( 'Email' );
        $form['pass']['#attributes']['placeholder'] = t( 'Password' );
        $form['name']['#attributes']['title'] = t( 'Введите email, указанный при регистрации' );
        $form['pass']['#attributes']['title'] = t( 'Введите пароль' );  
        $form['submit']['#default_value'] = t( 'Принять' ); // this line doesnt work((  
    }
}
Buttons and Submits (yes, they are different things in Form API) does not have default value. All you can set for submit is: #access, #after_build, #ajax, #attributes, #button_type (default: 'submit'), #disabled, #element_validate, #executes_submit_callback (default: TRUE), #limit_validation_errors, #name (default: 'op'), #parents, #post_render, #prefix, #pre_render, #process, #submit, #states, #suffix, #theme, #theme_wrappers, #tree, #type, #validate, #value, #weight

As you can see, no #default_value. As user is not supposed to be able to change that value, it's simply #value - no need for defaults.

Read more on Form API Reference.