diff --git a/hugolib/hugo_modules_test.go b/hugolib/hugo_modules_test.go
index ff3d01c04..464230437 100644
--- a/hugolib/hugo_modules_test.go
+++ b/hugolib/hugo_modules_test.go
@@ -701,10 +701,13 @@ Data: {{ .Site.Data }}
 
 	createSymlinks := func(baseDir, id string) {
 		for _, dir := range files.ComponentFolders {
-			c.Assert(os.Chdir(filepath.Join(baseDir, dir)), qt.IsNil)
-			c.Assert(os.Symlink("real", fmt.Sprintf("realsym%s", id)), qt.IsNil)
-			c.Assert(os.Chdir(filepath.Join(baseDir, dir, "real")), qt.IsNil)
-			c.Assert(os.Symlink("data.toml", fmt.Sprintf(filepath.FromSlash("datasym%s.toml"), id)), qt.IsNil)
+			// Issue #9119: private use language tags cannot exceed 8 characters.
+			if dir != "i18n" {
+				c.Assert(os.Chdir(filepath.Join(baseDir, dir)), qt.IsNil)
+				c.Assert(os.Symlink("real", fmt.Sprintf("realsym%s", id)), qt.IsNil)
+				c.Assert(os.Chdir(filepath.Join(baseDir, dir, "real")), qt.IsNil)
+				c.Assert(os.Symlink("data.toml", fmt.Sprintf(filepath.FromSlash("datasym%s.toml"), id)), qt.IsNil)
+			}
 		}
 	}
 
diff --git a/langs/i18n/translationProvider.go b/langs/i18n/translationProvider.go
index 9e82b18d9..44bd52f0c 100644
--- a/langs/i18n/translationProvider.go
+++ b/langs/i18n/translationProvider.go
@@ -93,6 +93,11 @@ func addTranslationFile(bundle *i18n.Bundle, r source.File) error {
 	lang := paths.Filename(name)
 	tag := language.Make(lang)
 	if tag == language.Und {
+		try := artificialLangTagPrefix + lang
+		_, err = language.Parse(try)
+		if err != nil {
+			return _errors.Errorf("%q %s.", try, err)
+		}
 		name = artificialLangTagPrefix + name
 	}