Document that mock request doesn't support Accept-Language header

This commit updates the Javadoc for getLocale() and getLocales() in
MockHttpServletRequest to point out that the mock implementation does
not comply with the the Servlet specification with regard to the
Accept-Language header.

Issue: SPR-12043

spring-test/src/main/java/org/springframework/mock/web/MockHttpServletRequest.java

@@ -634,11 +634,37 @@ public class MockHttpServletRequest implements HttpServletRequest {
 		this.locales.addAll(locales);
 	}
 
+	/**
+	 * Returns the first preferred {@linkplain Locale locale} configured
+	 * in this mock request.
+	 * <p>If no locales have been explicitly configured, the default,
+	 * preferred {@link Locale} for the <em>server</em> mocked by this
+	 * request is {@link Locale#ENGLISH}.
+	 * <p>In contrast to the Servlet specification, this mock implementation
+	 * does <strong>not</strong> take into consideration any locales
+	 * specified via the {@code Accept-Language} header.
+	 * @see javax.servlet.ServletRequest#getLocale()
+	 * @see #addPreferredLocale(Locale)
+	 * @see #setPreferredLocales(List)
+	 */
 	@Override
 	public Locale getLocale() {
 		return this.locales.get(0);
 	}
 
+	/**
+	 * Returns an {@linkplain Enumeration enumeration} of the preferred
+	 * {@linkplain Locale locales} configured in this mock request.
+	 * <p>If no locales have been explicitly configured, the default,
+	 * preferred {@link Locale} for the <em>server</em> mocked by this
+	 * request is {@link Locale#ENGLISH}.
+	 * <p>In contrast to the Servlet specification, this mock implementation
+	 * does <strong>not</strong> take into consideration any locales
+	 * specified via the {@code Accept-Language} header.
+	 * @see javax.servlet.ServletRequest#getLocales()
+	 * @see #addPreferredLocale(Locale)
+	 * @see #setPreferredLocales(List)
+	 */
 	@Override
 	public Enumeration<Locale> getLocales() {
 		return Collections.enumeration(this.locales);