Normalize i18n notice translation

_data/en/i18nnotice.yml

@@ -0,0 +1,4 @@
+i18n_notice: >
+  This document might be outdated relative to the documentation in English.
+  For the latest updates, please refer to the
+  <a href="{{ page.url | replace: '/en/', '/en/' }}">documentation in English</a>.

_includes/i18n-notice.html

@@ -1,2 +1,2 @@
-<p>{% include notice/notice-{{ page.lang }}.md %}</p>
+<p>{{ site.data[page.lang].i18nnotice.i18n_notice}}</p>
 <div id="close-i18n-notice-box" title="Close">✖</div>