Avoid panic in invalid language config

Fixes #11046

config/allconfig/alldecoders.go

@@ -245,14 +245,19 @@ var allDecoderSetups = map[string]decodeWeight{
 			if len(m) == 1 {
 				// In v0.112.4 we moved this to the language config, but it's very commmon for mono language sites to have this at the top level.
 				var first maps.Params
+				var ok bool
 				for _, v := range m {
-					first = v.(maps.Params)
+					first, ok = v.(maps.Params)
+					if ok {
 						break
 					}
+				}
+				if first != nil {
 					if _, found := first["languagecode"]; !found {
 						first["languagecode"] = p.p.GetString("languagecode")
 					}
 				}
+			}
 			p.c.Languages, err = langs.DecodeConfig(m)
 			if err != nil {
 				return err

hugolib/config_test.go

@@ -1067,10 +1067,12 @@ LanguageCode: {{ .Site.LanguageCode }}|{{ site.Language.LanguageCode }}|
 
 }
 
-// Issue 11047
-func TestConfigYamlNil(t *testing.T) {
+func TestConfigMiscPanics(t *testing.T) {
 	t.Parallel()
 
+	// Issue 11047,
+	t.Run("empty params", func(t *testing.T) {
+
 		files := `
 -- hugo.yaml --
 params:
@@ -1078,7 +1080,7 @@ params:
 Foo: {{ site.Params.foo }}|
 	
 		
-`
+	`
 		b := NewIntegrationTestBuilder(
 			IntegrationTestConfig{
 				T:           t,
@@ -1087,5 +1089,37 @@ Foo: {{ site.Params.foo }}|
 		).Build()
 
 		b.AssertFileContent("public/index.html", "Foo: |")
+	})
+
+	// Issue 11046
+	t.Run("invalid language setup", func(t *testing.T) {
+
+		files := `
+-- hugo.toml --
+baseURL = "https://example.org"
+languageCode = "en-us"
+title = "Blog of me"
+defaultContentLanguage = "en"
+
+[languages]
+	[en]
+	lang = "en"
+	languageName = "English"
+	weight = 1
+-- layouts/index.html --
+Foo: {{ site.Params.foo }}|
+	
+		
+	`
+		b, err := NewIntegrationTestBuilder(
+			IntegrationTestConfig{
+				T:           t,
+				TxtarString: files,
+			},
+		).BuildE()
+
+		b.Assert(err, qt.IsNotNil)
+		b.Assert(err.Error(), qt.Contains, "no languages")
+	})
 
 }

langs/config.go

@@ -14,6 +14,8 @@
 package langs
 
 import (
+	"errors"
+
 	"github.com/gohugoio/hugo/common/maps"
 	"github.com/mitchellh/mapstructure"
 )
@@ -46,5 +48,8 @@ func DecodeConfig(m map[string]any) (map[string]LanguageConfig, error) {
 	if err := mapstructure.WeakDecode(m, &langs); err != nil {
 		return nil, err
 	}
+	if len(langs) == 0 {
+		return nil, errors.New("no languages configured")
+	}
 	return langs, nil
 }