Fix the multilingual option's flag.

Babel fishes are awesome.
Using flags for languages is somewhat offensive,
since it's a gross, unfair simplification.
We'll remove the flags later.

user/themes/textbook/templates/partials/language-selector.html.twig

@@ -51,10 +51,10 @@
   <li>
     <a href="{{ '/polyglot-columns' ~ uri.path }}">
       {% if language_display.select == 'default' or language_display.select == 'flag' %}
-        <img alt="Rosetta" src="fr.png" />
+        <img alt="Rosetta" src="/{{ grav.locator.findResource('plugin://m3-p2/flags/xx.png', false) }}" />
       {% endif %}
       {% if language_display.select == 'default' or language_display.select == 'name' %}
-        Rosetta
+        Multilingual
       {% endif %}
     </a>
   </li>

user/themes/textbook/templates/polyglot-columns.html.twig

 {% extends 'partials/base.html.twig' %}
 
-{# page is irrelevant here #}
-{# use target_page, injected by m3-p2 plugin #}
+{# `page` is irrelevant here #}
+{# use `target_page`, injected by m3-p2 plugin #}
 
 {% block stylesheets %}
     {% do assets.addCss('theme://css/columns.css') %}