function load_my_styles() {
    wp_register_style( \'my-en-style1\', plugins_url( \'en-style1.css\', __FILE__ ) );
    wp_register_style( \'my-en-style2\', plugins_url( \'en-style2.css\', __FILE__ ) );

    wp_register_style( \'my-ja-style1\', plugins_url( \'ja-style1.css\', __FILE__ ) );
    wp_register_style( \'my-ja-style2\', plugins_url( \'ja-style2.css\', __FILE__ ) );

    $lang = preg_match( \'/^\\/ja\\//i\', $_SERVER[\'REQUEST_URI\'] ) ? \'ja\' : \'en\';
    wp_enqueue_style( "my-{$lang}-style1" );
    wp_enqueue_style( "my-{$lang}-style2" );
}
add_action( \'wp_enqueue_scripts\', \'load_my_styles\' );