Override "Accept-Language" header if WebDriver BiDi emulated language is present.

Author: lutien

fetch.bs

@@ -4659,10 +4659,28 @@ the response. [[!HTTP-CACHING]]
    <var>request</var>'s <a for=request>header list</a>.
   </ol>
 
- <li><p>If <var>request</var>'s <a for=request>header list</a>
- <a for="header list">does not contain</a> `<code>Accept-Language</code>`, then user agents should
- <a for="header list">append</a> (`<code>Accept-Language</code>, an appropriate
- <a for=/>header value</a>) to <var>request</var>'s <a for=request>header list</a>.
+ <li>
+  <p>If <var>request</var>'s <a for=request>header list</a> <a for="header list">does not contain</a> `<code>Accept-Language</code>`:
+
+  <ol>
+    <li>
+      <p>If <var>request</var>'s <a for=request>client</a> is non-null, then:
+
+      <ol>
+        <li><p>Let <var>emulatedLanguage</var> be the <span>WebDriver BiDi emulated language</span>
+        for <var>request</var>'s <a for=request>client</a>
+
+        <li><p>If <var>emulatedLanguage</var> is not null, <a for="header list">append</a>(`<code>Accept-Language</code>, <var>emulatedLanguage</var>)
+        to <var>request</var>'s <a for=request>header list</a>.
+
+        <li><p>Otherwise, user agents should <a for="header list">append</a> (`<code>Accept-Language</code>, an appropriate
+        <a for=/>header value</a>) to <var>request</var>'s <a for=request>header list</a>.
+      </ol>
+
+    <li><p>Otherwise, user agents should <a for="header list">append</a> (`<code>Accept-Language</code>, an appropriate
+        <a for=/>header value</a>) to <var>request</var>'s <a for=request>header list</a>.
+  </ol>
+
 
  <li>
   <p>If <var>request</var>'s <a for=request>internal priority</a> is null, then use