fix: calendar in Arabic (backport #26213) (#26215)

* Revert "fix(ar): render fullcalendar in english (#26207)"

This reverts commit e4ed1b9.

(cherry picked from commit 602ff82)

# Conflicts:
#	frappe/public/js/frappe/views/calendar/calendar.js

* fix(calendar): always use english dates for API calls

(cherry picked from commit 72d81af)

* chore: conflicts

---------

Co-authored-by: Ankush Menat <ankush@frappe.io>

cypress/integration/control_duration.js

@@ -20,11 +20,14 @@ context("Control Duration", () => {
 
 	it("should set duration", () => {
 		get_dialog_with_duration().as("dialog");
+		cy.wait(500);
 		cy.get(".frappe-control[data-fieldname=duration] input").first().click();
 		cy.get(".duration-input[data-duration=days]")
 			.type(45, { force: true })
 			.blur({ force: true });
+		cy.wait(500);
 		cy.get(".duration-input[data-duration=minutes]").type(30).blur({ force: true });
+		cy.wait(500);
 		cy.get(".frappe-control[data-fieldname=duration] input")
 			.first()
 			.should("have.value", "45d 30m");

frappe/public/js/frappe/views/calendar/calendar.js

@@ -245,7 +245,7 @@ frappe.views.Calendar = class Calendar {
 
 	get_system_datetime(date) {
 		date._offset = moment(date).tz(frappe.sys_defaults.time_zone)._offset;
-		return frappe.datetime.convert_to_system_tz(date);
+		return frappe.datetime.convert_to_system_tz(moment(date).locale("en"));
 	}
 	setup_options(defaults) {
 		var me = this;