Add Error method to I18nInput

Otherwise, we can not show the error message to the user, although it
assumes only the default language has error message, which is the case
for now, but….

pkg/form/input.go

@@ -74,3 +74,12 @@ func (input I18nInput) FillArray(array database.RecordArray) error {
 	}
 	return nil
 }
+
+func (input I18nInput) Error() string {
+	for _, inner := range input {
+		if inner.Error != nil {
+			return inner.Error.Error()
+		}
+	}
+	return ""
+}