diff --git a/hugolib/pages_language_merge_test.go b/hugolib/pages_language_merge_test.go
index 3b55a6288..b7c78836c 100644
--- a/hugolib/pages_language_merge_test.go
+++ b/hugolib/pages_language_merge_test.go
@@ -17,6 +17,7 @@ import (
 	"fmt"
 	"testing"
 
+	"github.com/gohugoio/hugo/resource"
 	"github.com/stretchr/testify/require"
 )
 
@@ -35,16 +36,16 @@ func TestMergeLanguages(t *testing.T) {
 	frSite := h.Sites[1]
 	nnSite := h.Sites[2]
 
-	assert.Equal(30, len(enSite.RegularPages))
+	assert.Equal(31, len(enSite.RegularPages))
 	assert.Equal(6, len(frSite.RegularPages))
-	assert.Equal(11, len(nnSite.RegularPages))
+	assert.Equal(12, len(nnSite.RegularPages))
 
 	for i := 0; i < 2; i++ {
 		mergedNN := nnSite.RegularPages.MergeByLanguage(enSite.RegularPages)
-		assert.Equal(30, len(mergedNN))
-		for i := 1; i <= 30; i++ {
+		assert.Equal(31, len(mergedNN))
+		for i := 1; i <= 31; i++ {
 			expectedLang := "en"
-			if i == 2 || i%3 == 0 {
+			if i == 2 || i%3 == 0 || i == 31 {
 				expectedLang = "nn"
 			}
 			p := mergedNN[i-1]
@@ -53,8 +54,8 @@ func TestMergeLanguages(t *testing.T) {
 	}
 
 	mergedFR := frSite.RegularPages.MergeByLanguage(enSite.RegularPages)
-	assert.Equal(30, len(mergedFR))
-	for i := 1; i <= 30; i++ {
+	assert.Equal(31, len(mergedFR))
+	for i := 1; i <= 31; i++ {
 		expectedLang := "en"
 		if i%5 == 0 {
 			expectedLang = "fr"
@@ -67,6 +68,17 @@ func TestMergeLanguages(t *testing.T) {
 	assert.Equal(4, len(firstNN.Sites()))
 	assert.Equal("en", firstNN.Sites().First().Language.Lang)
 
+	nnBundle := nnSite.getPage("page", "bundle")
+	enBundle := enSite.getPage("page", "bundle")
+
+	assert.Equal(6, len(enBundle.Resources))
+	assert.Equal(2, len(nnBundle.Resources))
+
+	var ri interface{} = nnBundle.Resources
+
+	// This looks less ugly in the templates ...
+	mergedNNResources := ri.(resource.ResourcesLanguageMerger).MergeByLanguage(enBundle.Resources)
+	assert.Equal(6, len(mergedNNResources))
 }
 
 func TestMergeLanguagesTemplate(t *testing.T) {
@@ -79,10 +91,16 @@ func TestMergeLanguagesTemplate(t *testing.T) {
 {{ if eq .Lang "nn" }}:
 {{ $enSite := index .Sites 0 }}
 {{ $frSite := index .Sites 1 }}
+{{ $nnBundle := .Site.GetPage "page" "bundle" }}
+{{ $enBundle := $enSite.GetPage "page" "bundle" }}
 {{ .Scratch.Set "pages" ($pages | lang.Merge $frSite.RegularPages| lang.Merge $enSite.RegularPages) }}
+{{ .Scratch.Set "pages2" (sort ($nnBundle.Resources | lang.Merge $enBundle.Resources) "Title") }}
 {{ end }}
 {{ $pages := .Scratch.Get "pages" }}
-{{ range $i, $p := $pages }}{{ add $i 1 }}: {{ .Path }} {{ .Lang }} | {{ end }}
+{{ $pages2 := .Scratch.Get "pages2" }}
+Pages1: {{ range $i, $p := $pages }}{{ add $i 1 }}: {{ .Path }} {{ .Lang }} | {{ end }}
+Pages2: {{ range $i, $p := $pages2 }}{{ add $i 1 }}: {{ .Title }} {{ .Lang }} | {{ end }}
+
 `,
 		"shortcodes/shortcode.html", "MyShort",
 		"shortcodes/lingo.html", "MyLingo",
@@ -91,7 +109,8 @@ func TestMergeLanguagesTemplate(t *testing.T) {
 	b.CreateSites()
 	b.Build(BuildCfg{})
 
-	b.AssertFileContent("public/nn/index.html", "p1.md en | 2: p2.nn.md nn | 3: p3.nn.md nn | 4: p4.md en | 5: p5.fr.md fr | 6: p6.nn.md nn | 7: p7.md en | 8: p8.md en | 9: p9.nn.md nn | 10: p10.fr.md fr | 11: p11.md en | 12: p12.nn.md nn | 13: p13.md en | 14: p14.md en | 15: p15.nn.md nn")
+	b.AssertFileContent("public/nn/index.html", "Pages1: 1: p1.md en | 2: p2.nn.md nn | 3: p3.nn.md nn | 4: p4.md en | 5: p5.fr.md fr | 6: p6.nn.md nn | 7: p7.md en | 8: p8.md en | 9: p9.nn.md nn | 10: p10.fr.md fr | 11: p11.md en | 12: p12.nn.md nn | 13: p13.md en | 14: p14.md en | 15: p15.nn.md nn")
+	b.AssertFileContent("public/nn/index.html", "Pages2: 1: doc100 en | 2: doc101 nn | 3: doc102 nn | 4: doc103 en | 5: doc104 en | 6: doc105 en")
 }
 
 func newTestSiteForLanguageMerge(t testing.TB, count int) *sitesBuilder {
@@ -126,6 +145,18 @@ date: "2018-02-28"
 		}
 	}
 
+	// See https://github.com/gohugoio/hugo/issues/4644
+	// Add a bundles
+	j := 100
+	contentPairs = append(contentPairs, []string{"bundle/index.md", fmt.Sprintf(contentTemplate, j, j)}...)
+	for i := 0; i < 6; i++ {
+		contentPairs = append(contentPairs, []string{fmt.Sprintf("bundle/pb%d.md", i), fmt.Sprintf(contentTemplate, i+j, i+j)}...)
+	}
+	contentPairs = append(contentPairs, []string{"bundle/index.nn.md", fmt.Sprintf(contentTemplate, j, j)}...)
+	for i := 1; i < 3; i++ {
+		contentPairs = append(contentPairs, []string{fmt.Sprintf("bundle/pb%d.nn.md", i), fmt.Sprintf(contentTemplate, i+j, i+j)}...)
+	}
+
 	builder.WithContent(contentPairs...)
 	return builder
 }
diff --git a/resource/resource.go b/resource/resource.go
index 12e1160cf..e92706803 100644
--- a/resource/resource.go
+++ b/resource/resource.go
@@ -34,10 +34,11 @@ import (
 )
 
 var (
-	_ Resource     = (*genericResource)(nil)
-	_ metaAssigner = (*genericResource)(nil)
-	_ Source       = (*genericResource)(nil)
-	_ Cloner       = (*genericResource)(nil)
+	_ Resource                = (*genericResource)(nil)
+	_ metaAssigner            = (*genericResource)(nil)
+	_ Source                  = (*genericResource)(nil)
+	_ Cloner                  = (*genericResource)(nil)
+	_ ResourcesLanguageMerger = (*Resources)(nil)
 )
 
 const DefaultResourceType = "unknown"
@@ -97,6 +98,16 @@ type Resource interface {
 	Content() (interface{}, error)
 }
 
+type ResourcesLanguageMerger interface {
+	MergeByLanguage(other Resources) Resources
+	// Needed for integration with the tpl package.
+	MergeByLanguageInterface(other interface{}) (interface{}, error)
+}
+
+type translatedResource interface {
+	TranslationKey() string
+}
+
 // Resources represents a slice of resources, which can be a mix of different types.
 // I.e. both pages and images etc.
 type Resources []Resource
@@ -222,6 +233,36 @@ func getGlob(pattern string) (glob.Glob, error) {
 
 }
 
+// MergeByLanguage adds missing translations in r1 from r2.
+func (r1 Resources) MergeByLanguage(r2 Resources) Resources {
+	result := append(Resources(nil), r1...)
+	m := make(map[string]bool)
+	for _, r := range r1 {
+		if translated, ok := r.(translatedResource); ok {
+			m[translated.TranslationKey()] = true
+		}
+	}
+
+	for _, r := range r2 {
+		if translated, ok := r.(translatedResource); ok {
+			if _, found := m[translated.TranslationKey()]; !found {
+				result = append(result, r)
+			}
+		}
+	}
+	return result
+}
+
+// MergeByLanguageInterface is the generic version of MergeByLanguage. It
+// is here just so it can be called from the tpl package.
+func (r1 Resources) MergeByLanguageInterface(in interface{}) (interface{}, error) {
+	r2, ok := in.(Resources)
+	if !ok {
+		return nil, fmt.Errorf("%T cannot be merged by language", in)
+	}
+	return r1.MergeByLanguage(r2), nil
+}
+
 type Spec struct {
 	*helpers.PathSpec