Encode "emulatedLanguage" before setting it as header value.

Author: lutien

fetch.bs

@@ -4669,8 +4669,8 @@ the response. [[!HTTP-CACHING]]
    <var>request</var>'s <a for=request>client</a>.
 
    <li><p>If <var>emulatedLanguage</var> is non-null, then <a for="header list">append</a>
-   (`<code>Accept-Language</code>, <var>emulatedLanguage</var>) to <var>request</var>'s
-   <a for=request>header list</a>.
+   (`<code>Accept-Language</code>, <var>emulatedLanguage</var>, <a>isomorphic encoded</a>)
+   to <var>request</var>'s <a for=request>header list</a>.
   </ol>
 
  <li><p>If <var>request</var>'s <a for=request>header list</a>