Content-Language Header is not added to http2 response

[11rx4f]

Problem Description

Content-Language Header is not added to http2 response despite using ServletResponse#setlocale().

setlocale.zip

• Servlet App:

  @WebServlet(urlPatterns = {"/sample"})
  public class App extends HttpServlet {
  public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException {
  res.setLocale(Locale.ENGLISH);
  res.getWriter().println("Hello, World!");
  }
  }

• request via http2, the response does not have the Content-Language header:

  
  # curl --http2 -s -k -i -X GET "http://localhost:8080/setlocale/sample"
  HTTP/1.1 101 Switching Protocols
  Server: Eclipse GlassFish  6.2.3 
  X-Powered-By: Servlet/5.0 JSP/3.0(Eclipse GlassFish  6.2.3  Java/Eclipse Foundation/11)
  Connection: Upgrade
  Upgrade: h2c

HTTP/2 200

Hello, World!

ServletResponse#setlocale() is described in [the servlet spec](https://javadoc.io/doc/jakarta.servlet/jakarta.servlet-api/latest/jakarta/servlet/ServletResponse.html#setLocale-java.util.Locale-) as bellow(*), so I think it is a bug.:

In the case of HTTP, the locale is communicated via the Content-Language header, the character encoding as part of the Content-Type header for text media types.

(*) When accessed via http1.1, Content-Language Header is added to response as below:

curl --http1.1 -s -k -i -X GET "http://localhost:8080/setlocale/sample"

HTTP/1.1 200 OK Server: Eclipse GlassFish 6.2.3 X-Powered-By: Servlet/5.0 JSP/3.0(Eclipse GlassFish 6.2.3 Java/Eclipse Foundation/11) Content-Language: en Content-Length: 14

Hello, World!

## Environment
* Server  
GlassFish (using grizzly-3.0.1 )
* JDK

java -version

openjdk version "11.0.12" 2021-07-20 OpenJDK Runtime Environment Temurin-11.0.12+7 (build 11.0.12+7) OpenJDK 64-Bit Server VM Temurin-11.0.12+7 (build 11.0.12+7, mixed mode)

* OS  
CentOS Linux release 7

## Steps to reproduce by glassfish
1. start-domain
2. deploy app setlocale.war

asadmin deploy setlocale.war

3. Access app by follwing command.

curl --http2 -s -k -i -X GET "http://localhost:8080/setlocale/sample"

## Impact of issue
This is violation of the API spec.  
https://javadoc.io/doc/jakarta.servlet/jakarta.servlet-api/latest/jakarta/servlet/ServletResponse.html#setLocale-java.util.Locale-