chore: rename country code to language code

#87 (comment)

Author: azu

_config.yml

@@ -38,7 +38,7 @@ redcarpet:
   extensions: [hard_wrap, with_toc_data]
 
 # multiple languages settings
-languages: ["jp", "kr"]
+languages: ["ja", "ko"]
 exclude_from_localizations: ["bower_components", "node_modules", "public"]
 
 gems:

_i18n/jp.yml renamed to _i18n/ja.yml

@@ -4,7 +4,7 @@ <h2>{% t description %}</h2>
     <nav class="lang-menu">
         <ul>
             <li><a href="{{ site.baseurl_root }}/" data-alt-href="{{ page.url | replace:'index.html','' }}">{% t global.japanese %}</a></li>
-            <li><a href="{{ site.baseurl_root }}/kr/" data-alt-href="/kr{{ page.url | replace:'index.html','' }}">{% t global.korean %}</a></li>
+            <li><a href="{{ site.baseurl_root }}/ko/" data-alt-href="/ko{{ page.url | replace:'index.html','' }}">{% t global.korean %}</a></li>
         </ul>
     </nav>
 </div>