How to change all “Post” texts in dahboard into “Article”?

You can update the override the post labels:

function wpse163462_rename_menu_post_to_article() {
    global $menu;
    global $submenu;
    $menu[5][0] = 'Articles';
    $submenu['edit.php'][5][0] = 'Articles';
    $submenu['edit.php'][10][0] = 'Add Articles';
    echo '';
}
function wpse163462_rename_post_to_article() {
        global $wp_post_types;
        $labels = &$wp_post_types['post']->labels;
        $labels->name="Articles";
        $labels->singular_name="Article";
        $labels->add_new = 'Add Article';
        $labels->add_new_item = 'Add Article';
        $labels->edit_item = 'Edit Article';
        $labels->new_item = 'Article';
        $labels->view_item = 'View Article';
        $labels->search_items="Search Articles";
        $labels->not_found = 'No Articles found';
        $labels->not_found_in_trash="No Articles found in Trash";
}
add_action( 'init', 'wpse163462_rename_post_to_article' );
add_action( 'admin_menu', 'wpse163462_rename_menu_post_to_article' );