Improve behavior of defaultContentLanguageInSubdir when only the default language is enabled

1 .Create sitemapindex in root of publishDir (will contain link to sitemap.xml in defaultContentLanguage site)
2. Create index.html in root of publishDir (will redirect to defaultContentLanguage site)

Fixes #11229

hugolib/config_test.go

@@ -1321,6 +1321,9 @@ Home.
 
 		b.AssertFileContent("public/en/index.html", "Home.")
 		b.AssertFileContent("public/en/foo/bar.txt", "Foo.")
+		b.AssertFileContent("public/index.html", "refresh")
+		b.AssertFileContent("public/sitemap.xml", "sitemapindex")
+		b.AssertFileContent("public/en/sitemap.xml", "urlset")
 	})
 
 	t.Run("Two languages, default in sub dir", func(t *testing.T) {
@@ -1351,6 +1354,9 @@ Home.
 
 		b.AssertFileContent("public/en/index.html", "Home.")
 		b.AssertFileContent("public/en/foo/bar.txt", "Foo.")
+		b.AssertFileContent("public/index.html", "refresh")
+		b.AssertFileContent("public/sitemap.xml", "sitemapindex")
+		b.AssertFileContent("public/en/sitemap.xml", "urlset")
 	})
 
 	t.Run("Two languages, default in root", func(t *testing.T) {
@@ -1381,6 +1387,8 @@ Home.
 
 		b.AssertFileContent("public/index.html", "Home.")
 		b.AssertFileContent("public/foo/bar.txt", "Foo.")
+		b.AssertFileContent("public/sitemap.xml", "sitemapindex")
+		b.AssertFileContent("public/en/sitemap.xml", "urlset")
 	})
 
 }

hugolib/hugo_sites.go

@@ -437,7 +437,7 @@ func (cfg *BuildCfg) shouldRender(p *pageState) bool {
 }
 
 func (h *HugoSites) renderCrossSitesSitemap() error {
-	if !h.isMultiLingual() || h.Conf.IsMultihost() {
+	if h.Conf.IsMultihost() || !(h.Conf.DefaultContentLanguageInSubdir() || h.Conf.IsMultiLingual()) {
 		return nil
 	}
 

hugolib/site_render.go

@@ -384,7 +384,7 @@ func (s *Site) renderAliases() error {
 // renderMainLanguageRedirect creates a redirect to the main language home,
 // depending on if it lives in sub folder (e.g. /en) or not.
 func (s *Site) renderMainLanguageRedirect() error {
-	if !s.h.isMultiLingual() || s.h.Conf.IsMultihost() {
+	if s.h.Conf.IsMultihost() || !(s.h.Conf.DefaultContentLanguageInSubdir() || s.h.Conf.IsMultiLingual()) {
 		// No need for a redirect
 		return nil
 	}