WordPress register_post_type() project with archive and rewite slug.

functions.php

<?php

function prefix_init() {
	register_post_type( 'project', array(
		'public'      => true,
		'label'       => __( 'Projects', 'text_domain' ),
		'has_archive' => true,
		'rewrite'     => array( 'slug' => _x( 'projects', 'slug', 'text_domain' ) ),
	) );
}

add_action( 'init', 'prefix_init' );