diff --git a/cmd/email_messages.go b/cmd/email_messages.go
index aef60c9..d07f7e9 100644
--- a/cmd/email_messages.go
+++ b/cmd/email_messages.go
@@ -54,7 +54,7 @@ func addEmailMessageFieldFlags(cmd *cobra.Command) {
 	cmd.Flags().String("reply-to", "", "Reply-to email address")
 	cmd.Flags().String("cc", "", "CC email address")
 	cmd.Flags().String("bcc", "", "BCC email address")
-	cmd.Flags().String("language-code", "", "Language/locale code (e.g. en-US)")
+	cmd.Flags().String("language-code", "", "Language code, ISO 639-1 (e.g. en, fr)")
 	cmd.Flags().String("email-format", "", `"styled" or "plain"`)
 	cmd.Flags().String("lmx", "", "LMX markup (inline)")
 	cmd.Flags().String("lmx-file", "", "Path to a file containing LMX markup")
diff --git a/cmd/email_messages_update_test.go b/cmd/email_messages_update_test.go
index 8cb220a..5e06cfc 100644
--- a/cmd/email_messages_update_test.go
+++ b/cmd/email_messages_update_test.go
@@ -173,7 +173,7 @@ func TestEmailMessageFieldParamsFromCmd(t *testing.T) {
 		cmd.ParseFlags([]string{
 			"--cc", "cc@acme.com",
 			"--bcc", "bcc@acme.com",
-			"--language-code", "en-US",
+			"--language-code", "en",
 		})
 		params, err := emailMessageFieldParamsFromCmd(cmd)
 		if err != nil {
@@ -185,7 +185,7 @@ func TestEmailMessageFieldParamsFromCmd(t *testing.T) {
 		if params.BCCEmail != "bcc@acme.com" {
 			t.Errorf("BCCEmail = %q", params.BCCEmail)
 		}
-		if params.LanguageCode != "en-US" {
+		if params.LanguageCode != "en" {
 			t.Errorf("LanguageCode = %q", params.LanguageCode)
 		}
 		for _, k := range []string{"ccEmail", "bccEmail", "languageCode"} {