Update Datepicker localisations and add missing ones. The nb_NO is just a renamed nb. The files are straight from upstream at https://github.com/jquery/jquery-ui/tree/main/ui/i18n

app/assets/javascripts-jquery-ui/datepicker-sv.js

@@ -0,0 +1,40 @@
+/* Swedish initialisation for the jQuery UI date picker plugin. */
+/* Written by Anders Ekdahl ( anders@nomadiz.se). */
+( function( factory ) {
+	"use strict";
+
+	if ( typeof define === "function" && define.amd ) {
+
+		// AMD. Register as an anonymous module.
+		define( [ "../widgets/datepicker" ], factory );
+	} else {
+
+		// Browser globals
+		factory( jQuery.datepicker );
+	}
+} )( function( datepicker ) {
+"use strict";
+
+datepicker.regional.sv = {
+	closeText: "Stäng",
+	prevText: "Förra",
+	nextText: "Nästa",
+	currentText: "Idag",
+	monthNames: [ "januari", "februari", "mars", "april", "maj", "juni",
+	"juli", "augusti", "september", "oktober", "november", "december" ],
+	monthNamesShort: [ "jan.", "feb.", "mars", "apr.", "maj", "juni",
+	"juli", "aug.", "sep.", "okt.", "nov.", "dec." ],
+	dayNamesShort: [ "sön", "mån", "tis", "ons", "tor", "fre", "lör" ],
+	dayNames: [ "söndag", "måndag", "tisdag", "onsdag", "torsdag", "fredag", "lördag" ],
+	dayNamesMin: [ "sö", "må", "ti", "on", "to", "fr", "lö" ],
+	weekHeader: "Ve",
+	dateFormat: "yy-mm-dd",
+	firstDay: 1,
+	isRTL: false,
+	showMonthAfterYear: false,
+	yearSuffix: "" };
+datepicker.setDefaults( datepicker.regional.sv );
+
+return datepicker.regional.sv;
+
+} );