diff -u b/core/includes/gettext.inc b/core/includes/gettext.inc
--- b/core/includes/gettext.inc
+++ b/core/includes/gettext.inc
@@ -408,7 +408,7 @@
         // If 'msgid' is empty, it means we got values for the header of the
         // file as per the structure of the Gettext format.
         $locale_plurals = variable_get('locale_translation_plurals', array());
-        if (count(array_filter($overwrite_options)) || empty($locale_plurals[$lang]['plurals'])) {
+        if (array_sum($overwrite_options) || empty($locale_plurals[$lang]['plurals'])) {
           // Since we only need to parse the header if we ought to update the
           // plural formula, only run this if we don't need to keep existing
           // data untouched or if we don't have an existing plural formula.
diff -u b/core/modules/locale/locale.test b/core/modules/locale/locale.test
--- b/core/modules/locale/locale.test
+++ b/core/modules/locale/locale.test
@@ -1485,7 +1485,7 @@
     return <<< EOF
 msgid ""
 msgstr ""
-"Project-Id-Version: Drupal 6\\n"
+"Project-Id-Version: Drupal 8\\n"
 "MIME-Version: 1.0\\n"
 "Content-Type: text/plain; charset=UTF-8\\n"
 "Content-Transfer-Encoding: 8bit\\n"
@@ -1504,7 +1504,7 @@
     return <<< EOF
 msgid ""
 msgstr ""
-"Project-Id-Version: Drupal 6\\n"
+"Project-Id-Version: Drupal 8\\n"
 "MIME-Version: 1.0\\n"
 "Content-Type: text/plain; charset=UTF-8\\n"
 "Content-Transfer-Encoding: 8bit\\n"