fix locale based weekday names

packages/lab/src/date-adapters/date-fns.ts

@@ -1,6 +1,7 @@
 import {
   type Locale,
   add as addDateFns,
+  addDays as addDaysFns,
   addMilliseconds as addMillisecondsDateFns,
   differenceInMilliseconds,
   endOfDay,
@@ -462,22 +463,16 @@ export class AdapterDateFns implements SaltDateAdapter<Date, Locale> {
   public getDayOfWeekName(
     dow: number,
     format: "long" | "short" | "narrow",
-    locale: Locale = enUS,
+    locale: Locale,
   ): string {
-    // Create a date representing the first day of the current week
-    const today = new Date();
-    const currentDay = today.getDay();
-    const diff = dow - currentDay;
-    const targetDate = new Date(today);
-    targetDate.setDate(today.getDate() + diff);
-
-    // Use Intl.DateTimeFormat to get the day name
-    const options: Intl.DateTimeFormatOptions = {
+    const startOfWeekDate = startOfWeek(new Date(), { locale: locale ?? this.locale });
+    const targetDate = addDaysFns(startOfWeekDate, dow);
+    return new Intl.DateTimeFormat( locale?.code ?? this.locale?.code, {
       weekday: format,
-    };
-    return targetDate.toLocaleDateString(locale.code, options);
+    }).format(targetDate);
   }
 
+
   /**
    * Gets the day of the month for a Date object.
    * @param date - The Date object.

packages/lab/src/date-adapters/dayjs.ts

@@ -3,6 +3,7 @@ import customParseFormat from "dayjs/plugin/customParseFormat";
 import timezone from "dayjs/plugin/timezone";
 import utc from "dayjs/plugin/utc";
 import weekday from "dayjs/plugin/weekday";
+import localeData from 'dayjs/plugin/localeData';
 import type {
   AdapterOptions,
   RecommendedFormats,
@@ -31,6 +32,7 @@ declare module "./types" {
 defaultDayjs.extend(utc);
 defaultDayjs.extend(timezone);
 defaultDayjs.extend(weekday);
+defaultDayjs.extend(localeData);
 
 // Dayjs expects Title-case months, so treats "jun" as invalid
 function capitalizeMonthInDate(value: string, format: string) {
@@ -500,14 +502,21 @@ export class AdapterDayjs implements SaltDateAdapter<Dayjs, string> {
    * Gets the name of the day of the week.
    * @param dow - The day of the week as a number (0-6).
    * @param format - The format for the day name ("long", "short", "narrow").
+   * @param locale - The locale to use
    * @returns The name of the day of the week.
    */
   public getDayOfWeekName(
     dow: number,
     format: "long" | "short" | "narrow",
+    locale?: string
   ): string {
-    const day = this.dayjs().weekday(dow);
-    return format === "narrow" ? day.format("dd")[0] : day.format("dddd");
+    const dayjsInstance = this.dayjs().locale(locale || this.locale);
+    if (format === "narrow") {
+      return dayjsInstance.localeData().weekdaysMin()[dow];
+    } else if (format === "short") {
+      return dayjsInstance.localeData().weekdaysShort()[dow];
+    }
+      return dayjsInstance.localeData().weekdays()[dow];
   }
 
   /**