Adding a Filter to Sidbar Login Plugin to Change Login Button Lable

In your funtions file, you need to create your function, name it as you like:

function my_changein_args ($my_form_args) {
  return array(
    'echo'           => true,
    'redirect'       => esc_url( apply_filters( 'sidebar_login_widget_login_redirect', $redirect ) ),
    'label_username' => __( 'Yourusernamelabel', 'sidebar-login' ),
    'label_password' => __( 'Yourpasswordlabel', 'sidebar-login' ),
    'label_remember' => __( 'Yourrememberlabel', 'sidebar-login' ),
    'label_log_in'   => __( 'Yourloginlabel', 'sidebar-login' ),
    'remember'       => $show_rememberme,
    'value_remember' => true
  );
}
add_filter( 'sidebar_login_widget_form_args', 'my_changein_args' ); 

Don’t forget to open and close PHP.