diff --git src/wp-includes/class-wp-locale.php src/wp-includes/class-wp-locale.php
index 50dd44847e..72adaecce0 100644
--- src/wp-includes/class-wp-locale.php
+++ src/wp-includes/class-wp-locale.php
@@ -128,22 +128,22 @@ class WP_Locale {
 		$this->weekday[6] = /* translators: Weekday. */ __( 'Saturday' );
 
 		// The first letter of each day.
-		$this->weekday_initial[ __( 'Sunday' ) ]    = /* translators: One-letter abbreviation of the weekday. */ _x( 'S', 'Sunday initial' );
-		$this->weekday_initial[ __( 'Monday' ) ]    = /* translators: One-letter abbreviation of the weekday. */ _x( 'M', 'Monday initial' );
-		$this->weekday_initial[ __( 'Tuesday' ) ]   = /* translators: One-letter abbreviation of the weekday. */ _x( 'T', 'Tuesday initial' );
-		$this->weekday_initial[ __( 'Wednesday' ) ] = /* translators: One-letter abbreviation of the weekday. */ _x( 'W', 'Wednesday initial' );
-		$this->weekday_initial[ __( 'Thursday' ) ]  = /* translators: One-letter abbreviation of the weekday. */ _x( 'T', 'Thursday initial' );
-		$this->weekday_initial[ __( 'Friday' ) ]    = /* translators: One-letter abbreviation of the weekday. */ _x( 'F', 'Friday initial' );
-		$this->weekday_initial[ __( 'Saturday' ) ]  = /* translators: One-letter abbreviation of the weekday. */ _x( 'S', 'Saturday initial' );
+		$this->weekday_initial[ $this->weekday[0] ] = /* translators: One-letter abbreviation of the weekday. */ _x( 'S', 'Sunday initial' );
+		$this->weekday_initial[ $this->weekday[1] ] = /* translators: One-letter abbreviation of the weekday. */ _x( 'M', 'Monday initial' );
+		$this->weekday_initial[ $this->weekday[2] ] = /* translators: One-letter abbreviation of the weekday. */ _x( 'T', 'Tuesday initial' );
+		$this->weekday_initial[ $this->weekday[3] ] = /* translators: One-letter abbreviation of the weekday. */ _x( 'W', 'Wednesday initial' );
+		$this->weekday_initial[ $this->weekday[4] ] = /* translators: One-letter abbreviation of the weekday. */ _x( 'T', 'Thursday initial' );
+		$this->weekday_initial[ $this->weekday[5] ] = /* translators: One-letter abbreviation of the weekday. */ _x( 'F', 'Friday initial' );
+		$this->weekday_initial[ $this->weekday[6] ] = /* translators: One-letter abbreviation of the weekday. */ _x( 'S', 'Saturday initial' );
 
 		// Abbreviations for each day.
-		$this->weekday_abbrev[ __( 'Sunday' ) ]    = /* translators: Three-letter abbreviation of the weekday. */ __( 'Sun' );
-		$this->weekday_abbrev[ __( 'Monday' ) ]    = /* translators: Ttree-letter abbreviation of the weekday. */ __( 'Mon' );
-		$this->weekday_abbrev[ __( 'Tuesday' ) ]   = /* translators: Three-letter abbreviation of the weekday. */ __( 'Tue' );
-		$this->weekday_abbrev[ __( 'Wednesday' ) ] = /* translators: Three-letter abbreviation of the weekday. */ __( 'Wed' );
-		$this->weekday_abbrev[ __( 'Thursday' ) ]  = /* translators: Three-letter abbreviation of the weekday. */ __( 'Thu' );
-		$this->weekday_abbrev[ __( 'Friday' ) ]    = /* translators: Three-letter abbreviation of the weekday. */ __( 'Fri' );
-		$this->weekday_abbrev[ __( 'Saturday' ) ]  = /* translators: Three-letter abbreviation of the weekday. */ __( 'Sat' );
+		$this->weekday_abbrev[ $this->weekday[0] ] = /* translators: Three-letter abbreviation of the weekday. */ __( 'Sun' );
+		$this->weekday_abbrev[ $this->weekday[1] ] = /* translators: Ttree-letter abbreviation of the weekday. */ __( 'Mon' );
+		$this->weekday_abbrev[ $this->weekday[2] ] = /* translators: Three-letter abbreviation of the weekday. */ __( 'Tue' );
+		$this->weekday_abbrev[ $this->weekday[3] ] = /* translators: Three-letter abbreviation of the weekday. */ __( 'Wed' );
+		$this->weekday_abbrev[ $this->weekday[4] ] = /* translators: Three-letter abbreviation of the weekday. */ __( 'Thu' );
+		$this->weekday_abbrev[ $this->weekday[5] ] = /* translators: Three-letter abbreviation of the weekday. */ __( 'Fri' );
+		$this->weekday_abbrev[ $this->weekday[6] ] = /* translators: Three-letter abbreviation of the weekday. */ __( 'Sat' );
 
 		// The months.
 		$this->month['01'] = /* translators: Month name. */ __( 'January' );
@@ -174,18 +174,18 @@ class WP_Locale {
 		$this->month_genitive['12'] = /* translators: Month name, genitive. */ _x( 'December', 'genitive' );
 
 		// Abbreviations for each month.
-		$this->month_abbrev[ __( 'January' ) ]   = /* translators: Three-letter abbreviation of the month. */ _x( 'Jan', 'January abbreviation' );
-		$this->month_abbrev[ __( 'February' ) ]  = /* translators: Three-letter abbreviation of the month. */ _x( 'Feb', 'February abbreviation' );
-		$this->month_abbrev[ __( 'March' ) ]     = /* translators: Three-letter abbreviation of the month. */ _x( 'Mar', 'March abbreviation' );
-		$this->month_abbrev[ __( 'April' ) ]     = /* translators: Three-letter abbreviation of the month. */ _x( 'Apr', 'April abbreviation' );
-		$this->month_abbrev[ __( 'May' ) ]       = /* translators: Three-letter abbreviation of the month. */ _x( 'May', 'May abbreviation' );
-		$this->month_abbrev[ __( 'June' ) ]      = /* translators: Three-letter abbreviation of the month. */ _x( 'Jun', 'June abbreviation' );
-		$this->month_abbrev[ __( 'July' ) ]      = /* translators: Three-letter abbreviation of the month. */ _x( 'Jul', 'July abbreviation' );
-		$this->month_abbrev[ __( 'August' ) ]    = /* translators: Three-letter abbreviation of the month. */ _x( 'Aug', 'August abbreviation' );
-		$this->month_abbrev[ __( 'September' ) ] = /* translators: Three-letter abbreviation of the month. */ _x( 'Sep', 'September abbreviation' );
-		$this->month_abbrev[ __( 'October' ) ]   = /* translators: Three-letter abbreviation of the month. */ _x( 'Oct', 'October abbreviation' );
-		$this->month_abbrev[ __( 'November' ) ]  = /* translators: Three-letter abbreviation of the month. */ _x( 'Nov', 'November abbreviation' );
-		$this->month_abbrev[ __( 'December' ) ]  = /* translators: Three-letter abbreviation of the month. */ _x( 'Dec', 'December abbreviation' );
+		$this->month_abbrev[ $this->month['01'] ] = /* translators: Three-letter abbreviation of the month. */ _x( 'Jan', 'January abbreviation' );
+		$this->month_abbrev[ $this->month['02'] ] = /* translators: Three-letter abbreviation of the month. */ _x( 'Feb', 'February abbreviation' );
+		$this->month_abbrev[ $this->month['03'] ] = /* translators: Three-letter abbreviation of the month. */ _x( 'Mar', 'March abbreviation' );
+		$this->month_abbrev[ $this->month['04'] ] = /* translators: Three-letter abbreviation of the month. */ _x( 'Apr', 'April abbreviation' );
+		$this->month_abbrev[ $this->month['05'] ] = /* translators: Three-letter abbreviation of the month. */ _x( 'May', 'May abbreviation' );
+		$this->month_abbrev[ $this->month['06'] ] = /* translators: Three-letter abbreviation of the month. */ _x( 'Jun', 'June abbreviation' );
+		$this->month_abbrev[ $this->month['07'] ] = /* translators: Three-letter abbreviation of the month. */ _x( 'Jul', 'July abbreviation' );
+		$this->month_abbrev[ $this->month['08'] ] = /* translators: Three-letter abbreviation of the month. */ _x( 'Aug', 'August abbreviation' );
+		$this->month_abbrev[ $this->month['09'] ] = /* translators: Three-letter abbreviation of the month. */ _x( 'Sep', 'September abbreviation' );
+		$this->month_abbrev[ $this->month['10'] ] = /* translators: Three-letter abbreviation of the month. */ _x( 'Oct', 'October abbreviation' );
+		$this->month_abbrev[ $this->month['11'] ] = /* translators: Three-letter abbreviation of the month. */ _x( 'Nov', 'November abbreviation' );
+		$this->month_abbrev[ $this->month['12'] ] = /* translators: Three-letter abbreviation of the month. */ _x( 'Dec', 'December abbreviation' );
 
 		// The meridiems.
 		$this->meridiem['am'] = __( 'am' );