fix(datetime): preferWheel respects column ordering by locale

core/src/components/datetime/datetime.tsx

@@ -1522,7 +1522,27 @@ export class Datetime implements ComponentInterface {
       ? getYearColumnData(this.todayParts, this.minParts, this.maxParts, this.parsedYearValues)
       : [];
 
-    return [this.renderMonthPickerColumn(months), this.renderDayPickerColumn(days), this.renderYearPickerColumn(years)];
+    /**
+     * Certain locales show the day before the month.
+     */
+    const showMonthFirst = isMonthFirstLocale(this.locale, { month: 'numeric', day: 'numeric' });
+
+    let renderArray = [];
+    if (showMonthFirst) {
+      renderArray = [
+        this.renderMonthPickerColumn(months),
+        this.renderDayPickerColumn(days),
+        this.renderYearPickerColumn(years),
+      ];
+    } else {
+      renderArray = [
+        this.renderDayPickerColumn(days),
+        this.renderMonthPickerColumn(months),
+        this.renderYearPickerColumn(years),
+      ];
+    }
+
+    return renderArray;
   }
 
   private renderDayPickerColumn(days: PickerColumnItem[]) {

core/src/components/datetime/test/prefer-wheel/datetime.e2e.ts

@@ -89,26 +89,64 @@ test.describe('datetime: prefer wheel', () => {
       expect(await yearValues.count()).toBe(3);
       expect(await dayValues.count()).toBe(5);
     });
-    test('should correctly localize the date data', async ({ page }) => {
-      await page.setContent(`
-        <ion-datetime
-          presentation="date"
-          prefer-wheel="true"
-          locale="ja-JP"
-          min="2022-01-01"
-          max="2022-03-01"
-          day-values="1,2,3"
-          value="2022-01-01"
-        ></ion-datetime>
-      `);
-
-      await page.waitForSelector('.datetime-ready');
-
-      const monthValues = page.locator('.month-column .picker-item:not(.picker-item-empty)');
-      const dayValues = page.locator('.day-column .picker-item:not(.picker-item-empty)');
-
-      expect(monthValues).toHaveText(['1月', '2月', '3月']);
-      expect(dayValues).toHaveText(['1日', '2日', '3日']);
+    test.describe('datetime: date wheel localization', () => {
+      test('should correctly localize the date data', async ({ page }) => {
+        await page.setContent(`
+          <ion-datetime
+            presentation="date"
+            prefer-wheel="true"
+            locale="ja-JP"
+            min="2022-01-01"
+            max="2022-03-01"
+            day-values="1,2,3"
+            value="2022-01-01"
+          ></ion-datetime>
+        `);
+
+        await page.waitForSelector('.datetime-ready');
+
+        const monthValues = page.locator('.month-column .picker-item:not(.picker-item-empty)');
+        const dayValues = page.locator('.day-column .picker-item:not(.picker-item-empty)');
+
+        expect(monthValues).toHaveText(['1月', '2月', '3月']);
+        expect(dayValues).toHaveText(['1日', '2日', '3日']);
+      });
+      test('should render the columns according to locale - en-US', async ({ page }) => {
+        await page.setContent(`
+          <ion-datetime
+            presentation="date"
+            prefer-wheel="true"
+            locale="en-US"
+            value="2022-01-01"
+          ></ion-datetime>
+        `);
+
+        await page.waitForSelector('.datetime-ready');
+
+        const columns = page.locator('ion-picker-column-internal');
+
+        await expect(columns.nth(0)).toHaveClass(/month-column/);
+        await expect(columns.nth(1)).toHaveClass(/day-column/);
+        await expect(columns.nth(2)).toHaveClass(/year-column/);
+      });
+      test('should render the columns according to locale - en-GB', async ({ page }) => {
+        await page.setContent(`
+          <ion-datetime
+            presentation="date"
+            prefer-wheel="true"
+            locale="en-GB"
+            value="2022-01-01"
+          ></ion-datetime>
+        `);
+
+        await page.waitForSelector('.datetime-ready');
+
+        const columns = page.locator('ion-picker-column-internal');
+
+        await expect(columns.nth(0)).toHaveClass(/day-column/);
+        await expect(columns.nth(1)).toHaveClass(/month-column/);
+        await expect(columns.nth(2)).toHaveClass(/year-column/);
+      });
     });
   });
   test.describe('datetime: date-time wheel rendering', () => {

core/src/components/datetime/utils/helpers.ts

@@ -74,8 +74,19 @@ export const getNumDaysInMonth = (month: number, year: number) => {
  * others display year then month.
  * We can use Intl.DateTimeFormat to determine
  * the ordering for each locale.
+ * The formatOptions param can be used to customize
+ * which pieces of a date to compare against the month
+ * with. For example, some locales render dd/mm/yyyy
+ * while others render mm/dd/yyyy. This function can be
+ * used for variations of the same "month first" check.
  */
-export const isMonthFirstLocale = (locale: string) => {
+export const isMonthFirstLocale = (
+  locale: string,
+  formatOptions: Intl.DateTimeFormatOptions = {
+    month: 'numeric',
+    year: 'numeric',
+  }
+) => {
   /**
    * By setting month and year we guarantee that only
    * month, year, and literal (slashes '/', for example)
@@ -88,7 +99,7 @@ export const isMonthFirstLocale = (locale: string) => {
    *
    * This ordering can be controlled by customizing the locale property.
    */
-  const parts = new Intl.DateTimeFormat(locale, { month: 'numeric', year: 'numeric' }).formatToParts(new Date());
+  const parts = new Intl.DateTimeFormat(locale, formatOptions).formatToParts(new Date());
 
   return parts[0].type === 'month';
 };