diff --git a/package.json b/package.json
index 2db10f8920..891ac01e35 100644
--- a/package.json
+++ b/package.json
@@ -137,6 +137,7 @@
     "vis-network": "^8.5.4",
     "vue": "^2.6.12",
     "vue2-daterange-picker": "^0.5.1",
+    "weekstart": "^1.1.0",
     "workbox-cacheable-response": "^6.4.2",
     "workbox-core": "^6.4.2",
     "workbox-expiration": "^6.4.2",
diff --git a/src/common/datetime/first_weekday.ts b/src/common/datetime/first_weekday.ts
new file mode 100644
index 0000000000..48b7b75261
--- /dev/null
+++ b/src/common/datetime/first_weekday.ts
@@ -0,0 +1,29 @@
+import { getWeekStartByLocale } from "weekstart";
+import { FrontendLocaleData, FirstWeekday } from "../../data/translation";
+
+export const weekdays = [
+  "sunday",
+  "monday",
+  "tuesday",
+  "wednesday",
+  "thursday",
+  "friday",
+  "saturday",
+] as const;
+
+export const firstWeekdayIndex = (locale: FrontendLocaleData): number => {
+  if (locale.first_weekday === FirstWeekday.language) {
+    // @ts-ignore
+    if ("weekInfo" in Intl.Locale.prototype) {
+      // @ts-ignore
+      return new Intl.Locale(locale.language).weekInfo.firstDay % 7;
+    }
+    return getWeekStartByLocale(locale.language) % 7;
+  }
+  return weekdays.indexOf(locale.first_weekday);
+};
+
+export const firstWeekday = (locale: FrontendLocaleData) => {
+  const index = firstWeekdayIndex(locale);
+  return weekdays[index];
+};
diff --git a/src/components/date-range-picker.ts b/src/components/date-range-picker.ts
index 7224e047f1..8cb7610ee1 100644
--- a/src/components/date-range-picker.ts
+++ b/src/components/date-range-picker.ts
@@ -33,6 +33,10 @@ const Component = Vue.extend({
         return new Date();
       },
     },
+    firstDay: {
+      type: Number,
+      default: 1,
+    },
   },
   render(createElement) {
     // @ts-ignore
@@ -48,6 +52,10 @@ const Component = Vue.extend({
         disabled: this.disabled,
         // @ts-ignore
         ranges: this.ranges ? {} : false,
+        "locale-data": {
+          // @ts-ignore
+          firstDay: this.firstDay,
+        },
       },
       model: {
         value: {
diff --git a/src/components/ha-date-input.ts b/src/components/ha-date-input.ts
index c776519ceb..bd542fb797 100644
--- a/src/components/ha-date-input.ts
+++ b/src/components/ha-date-input.ts
@@ -2,6 +2,7 @@ import { mdiCalendar } from "@mdi/js";
 import { css, CSSResultGroup, html, LitElement } from "lit";
 import { customElement, property } from "lit/decorators";
 import { formatDateNumeric } from "../common/datetime/format_date";
+import { firstWeekdayIndex } from "../common/datetime/first_weekday";
 import { fireEvent } from "../common/dom/fire_event";
 import { HomeAssistant } from "../types";
 import "./ha-svg-icon";
@@ -14,6 +15,7 @@ export interface datePickerDialogParams {
   min?: string;
   max?: string;
   locale?: string;
+  firstWeekday?: number;
   onChange: (value: string) => void;
 }
 
@@ -67,6 +69,7 @@ export class HaDateInput extends LitElement {
       value: this.value,
       onChange: (value) => this._valueChanged(value),
       locale: this.locale.language,
+      firstWeekday: firstWeekdayIndex(this.locale),
     });
   }
 
diff --git a/src/components/ha-date-range-picker.ts b/src/components/ha-date-range-picker.ts
index 40e5d0d1d7..3353d5db26 100644
--- a/src/components/ha-date-range-picker.ts
+++ b/src/components/ha-date-range-picker.ts
@@ -14,6 +14,7 @@ import {
 import { customElement, property } from "lit/decorators";
 import { formatDateTime } from "../common/datetime/format_date_time";
 import { useAmPm } from "../common/datetime/use_am_pm";
+import { firstWeekdayIndex } from "../common/datetime/first_weekday";
 import { computeRTLDirection } from "../common/util/compute_rtl";
 import { HomeAssistant } from "../types";
 import "./date-range-picker";
@@ -58,6 +59,7 @@ export class HaDateRangePicker extends LitElement {
         start-date=${this.startDate}
         end-date=${this.endDate}
         ?ranges=${this.ranges !== undefined}
+        first-day=${firstWeekdayIndex(this.hass.locale)}
       >
         <div slot="input" class="date-range-inputs">
           <ha-svg-icon .path=${mdiCalendar}></ha-svg-icon>
diff --git a/src/components/ha-dialog-date-picker.ts b/src/components/ha-dialog-date-picker.ts
index 2cb229db7b..110b088928 100644
--- a/src/components/ha-dialog-date-picker.ts
+++ b/src/components/ha-dialog-date-picker.ts
@@ -40,6 +40,7 @@ export class HaDialogDatePicker extends LitElement {
         .max=${this._params.max}
         .locale=${this._params.locale}
         @datepicker-value-updated=${this._valueChanged}
+        .firstDayOfWeek=${this._params.firstWeekday}
       ></app-datepicker>
       <mwc-button slot="secondaryAction" @click=${this._setToday}
         >today</mwc-button
diff --git a/src/data/translation.ts b/src/data/translation.ts
index cadcfe0ca7..e47d9d031b 100644
--- a/src/data/translation.ts
+++ b/src/data/translation.ts
@@ -17,10 +17,22 @@ export enum TimeFormat {
   twenty_four = "24",
 }
 
+export enum FirstWeekday {
+  language = "language",
+  monday = "monday",
+  tuesday = "tuesday",
+  wednesday = "wednesday",
+  thursday = "thursday",
+  friday = "friday",
+  saturday = "saturday",
+  sunday = "sunday",
+}
+
 export interface FrontendLocaleData {
   language: string;
   number_format: NumberFormat;
   time_format: TimeFormat;
+  first_weekday: FirstWeekday;
 }
 
 declare global {
diff --git a/src/fake_data/provide_hass.ts b/src/fake_data/provide_hass.ts
index e71667675e..8a6d1c36f1 100644
--- a/src/fake_data/provide_hass.ts
+++ b/src/fake_data/provide_hass.ts
@@ -6,7 +6,7 @@ import {
 import { fireEvent } from "../common/dom/fire_event";
 import { computeLocalize } from "../common/translations/localize";
 import { DEFAULT_PANEL } from "../data/panel";
-import { NumberFormat, TimeFormat } from "../data/translation";
+import { FirstWeekday, NumberFormat, TimeFormat } from "../data/translation";
 import { translationMetadata } from "../resources/translations-metadata";
 import { HomeAssistant } from "../types";
 import { getLocalLanguage, getTranslation } from "../util/common-translation";
@@ -224,6 +224,7 @@ export const provideHass = (
       language: localLanguage,
       number_format: NumberFormat.language,
       time_format: TimeFormat.language,
+      first_weekday: FirstWeekday.language,
     },
     resources: null as any,
     localize: () => "",
diff --git a/src/panels/calendar/ha-full-calendar.ts b/src/panels/calendar/ha-full-calendar.ts
index 8b2b2ad4b5..50c393bce5 100644
--- a/src/panels/calendar/ha-full-calendar.ts
+++ b/src/panels/calendar/ha-full-calendar.ts
@@ -37,6 +37,7 @@ import type {
   HomeAssistant,
   ToggleButton,
 } from "../../types";
+import { firstWeekdayIndex } from "../../common/datetime/first_weekday";
 
 declare global {
   interface HTMLElementTagNameMap {
@@ -214,6 +215,7 @@ export class HAFullCalendar extends LitElement {
     const config: CalendarOptions = {
       ...defaultFullCalendarConfig,
       locale: this.hass.language,
+      firstDay: firstWeekdayIndex(this.hass.locale),
       initialView: this.initialView,
       eventTimeFormat: {
         hour: useAmPm(this.hass.locale) ? "numeric" : "2-digit",
diff --git a/src/panels/config/automation/condition/types/ha-automation-condition-time.ts b/src/panels/config/automation/condition/types/ha-automation-condition-time.ts
index e2b2301b21..ce08d1654d 100644
--- a/src/panels/config/automation/condition/types/ha-automation-condition-time.ts
+++ b/src/panels/config/automation/condition/types/ha-automation-condition-time.ts
@@ -1,15 +1,17 @@
 import { html, LitElement } from "lit";
 import { customElement, property, state } from "lit/decorators";
 import memoizeOne from "memoize-one";
+import { firstWeekdayIndex } from "../../../../../common/datetime/first_weekday";
 import { fireEvent } from "../../../../../common/dom/fire_event";
-import type { TimeCondition } from "../../../../../data/automation";
-import type { HomeAssistant } from "../../../../../types";
-import type { ConditionElement } from "../ha-automation-condition-row";
 import type { LocalizeFunc } from "../../../../../common/translations/localize";
 import "../../../../../components/ha-form/ha-form";
 import type { SchemaUnion } from "../../../../../components/ha-form/types";
+import type { TimeCondition } from "../../../../../data/automation";
+import { FrontendLocaleData } from "../../../../../data/translation";
+import type { HomeAssistant } from "../../../../../types";
+import type { ConditionElement } from "../ha-automation-condition-row";
 
-const DAYS = ["mon", "tue", "wed", "thu", "fri", "sat", "sun"] as const;
+const DAYS = ["sun", "mon", "tue", "wed", "thu", "fri", "sat"] as const;
 
 @customElement("ha-automation-condition-time")
 export class HaTimeCondition extends LitElement implements ConditionElement {
@@ -30,10 +32,15 @@ export class HaTimeCondition extends LitElement implements ConditionElement {
   private _schema = memoizeOne(
     (
       localize: LocalizeFunc,
+      locale: FrontendLocaleData,
       inputModeAfter?: boolean,
       inputModeBefore?: boolean
-    ) =>
-      [
+    ) => {
+      const dayIndex = firstWeekdayIndex(locale);
+      const sortedDays = DAYS.slice(dayIndex, DAYS.length).concat(
+        DAYS.slice(0, dayIndex)
+      );
+      return [
         {
           name: "mode_after",
           type: "select",
@@ -87,7 +94,7 @@ export class HaTimeCondition extends LitElement implements ConditionElement {
         {
           type: "multi_select",
           name: "weekday",
-          options: DAYS.map(
+          options: sortedDays.map(
             (day) =>
               [
                 day,
@@ -97,7 +104,8 @@ export class HaTimeCondition extends LitElement implements ConditionElement {
               ] as const
           ),
         },
-      ] as const
+      ] as const;
+    }
   );
 
   protected render() {
@@ -110,6 +118,7 @@ export class HaTimeCondition extends LitElement implements ConditionElement {
 
     const schema = this._schema(
       this.hass.localize,
+      this.hass.locale,
       inputModeAfter,
       inputModeBefore
     );
diff --git a/src/panels/config/helpers/forms/ha-schedule-form.ts b/src/panels/config/helpers/forms/ha-schedule-form.ts
index 7aa682ae5c..2c238c1ef4 100644
--- a/src/panels/config/helpers/forms/ha-schedule-form.ts
+++ b/src/panels/config/helpers/forms/ha-schedule-form.ts
@@ -19,6 +19,7 @@ import {
 import { customElement, property, state } from "lit/decorators";
 import { formatTime24h } from "../../../../common/datetime/format_time";
 import { useAmPm } from "../../../../common/datetime/use_am_pm";
+import { firstWeekdayIndex } from "../../../../common/datetime/first_weekday";
 import { fireEvent } from "../../../../common/dom/fire_event";
 import "../../../../components/ha-icon-picker";
 import "../../../../components/ha-textfield";
@@ -169,6 +170,7 @@ class HaScheduleForm extends LitElement {
     const config: CalendarOptions = {
       ...defaultFullCalendarConfig,
       locale: this.hass.language,
+      firstDay: firstWeekdayIndex(this.hass.locale),
       slotLabelFormat: {
         hour: "numeric",
         minute: undefined,
diff --git a/src/panels/profile/ha-panel-profile.ts b/src/panels/profile/ha-panel-profile.ts
index 7ecc99b68f..2d709dbc61 100644
--- a/src/panels/profile/ha-panel-profile.ts
+++ b/src/panels/profile/ha-panel-profile.ts
@@ -24,6 +24,7 @@ import "./ha-force-narrow-row";
 import "./ha-long-lived-access-tokens-card";
 import "./ha-mfa-modules-card";
 import "./ha-pick-dashboard-row";
+import "./ha-pick-first-weekday-row";
 import "./ha-pick-language-row";
 import "./ha-pick-number-format-row";
 import "./ha-pick-theme-row";
@@ -100,6 +101,10 @@ class HaPanelProfile extends LitElement {
               .narrow=${this.narrow}
               .hass=${this.hass}
             ></ha-pick-time-format-row>
+            <ha-pick-first-weekday-row
+              .narrow=${this.narrow}
+              .hass=${this.hass}
+            ></ha-pick-first-weekday-row>
             <ha-pick-theme-row
               .narrow=${this.narrow}
               .hass=${this.hass}
diff --git a/src/panels/profile/ha-pick-first-weekday-row.ts b/src/panels/profile/ha-pick-first-weekday-row.ts
new file mode 100644
index 0000000000..08b09af9a9
--- /dev/null
+++ b/src/panels/profile/ha-pick-first-weekday-row.ts
@@ -0,0 +1,70 @@
+import "@material/mwc-list/mwc-list-item";
+import { html, LitElement, TemplateResult } from "lit";
+import { customElement, property } from "lit/decorators";
+import { firstWeekday } from "../../common/datetime/first_weekday";
+import { fireEvent } from "../../common/dom/fire_event";
+import "../../components/ha-select";
+import "../../components/ha-settings-row";
+import { FirstWeekday } from "../../data/translation";
+import { HomeAssistant } from "../../types";
+
+@customElement("ha-pick-first-weekday-row")
+class FirstWeekdayRow extends LitElement {
+  @property({ attribute: false }) public hass!: HomeAssistant;
+
+  @property() public narrow!: boolean;
+
+  protected render(): TemplateResult {
+    return html`
+      <ha-settings-row .narrow=${this.narrow}>
+        <span slot="heading">
+          ${this.hass.localize("ui.panel.profile.first_weekday.header")}
+        </span>
+        <span slot="description">
+          ${this.hass.localize("ui.panel.profile.first_weekday.description")}
+        </span>
+        <ha-select
+          .label=${this.hass.localize(
+            "ui.panel.profile.first_weekday.dropdown_label"
+          )}
+          .disabled=${this.hass.locale === undefined}
+          .value=${this.hass.locale.first_weekday}
+          @selected=${this._handleFormatSelection}
+        >
+          ${Object.values(FirstWeekday).map((day) => {
+            const value = this.hass.localize(
+              `ui.panel.profile.first_weekday.values.${day}`
+            );
+            const twoLine = day === FirstWeekday.language;
+            return html`
+              <mwc-list-item .value=${day} .twoline=${twoLine}>
+                <span>${value}</span>
+                ${twoLine
+                  ? html`
+                      <span slot="secondary"
+                        >${this.hass.localize(
+                          `ui.panel.profile.first_weekday.values.${firstWeekday(
+                            this.hass.locale
+                          )}`
+                        )}</span
+                      >
+                    `
+                  : ""}
+              </mwc-list-item>
+            `;
+          })}
+        </ha-select>
+      </ha-settings-row>
+    `;
+  }
+
+  private async _handleFormatSelection(ev) {
+    fireEvent(this, "hass-first-weekday-select", ev.target.value);
+  }
+}
+
+declare global {
+  interface HTMLElementTagNameMap {
+    "ha-pick-first-weekday-row": FirstWeekdayRow;
+  }
+}
diff --git a/src/state/connection-mixin.ts b/src/state/connection-mixin.ts
index 5d896360c8..dab61ccbb1 100644
--- a/src/state/connection-mixin.ts
+++ b/src/state/connection-mixin.ts
@@ -15,7 +15,7 @@ import { subscribeFrontendUserData } from "../data/frontend";
 import { forwardHaptic } from "../data/haptics";
 import { DEFAULT_PANEL } from "../data/panel";
 import { serviceCallWillDisconnect } from "../data/service";
-import { NumberFormat, TimeFormat } from "../data/translation";
+import { FirstWeekday, NumberFormat, TimeFormat } from "../data/translation";
 import { subscribePanels } from "../data/ws-panels";
 import { translationMetadata } from "../resources/translations-metadata";
 import { Constructor, HomeAssistant, ServiceCallResponse } from "../types";
@@ -58,6 +58,7 @@ export const connectionMixin = <T extends Constructor<HassBaseEl>>(
           language,
           number_format: NumberFormat.language,
           time_format: TimeFormat.language,
+          first_weekday: FirstWeekday.language,
         },
         resources: null as any,
         localize: () => "",
diff --git a/src/state/translations-mixin.ts b/src/state/translations-mixin.ts
index b84e711548..b0848fcb4e 100644
--- a/src/state/translations-mixin.ts
+++ b/src/state/translations-mixin.ts
@@ -6,6 +6,7 @@ import {
 } from "../common/util/compute_rtl";
 import { debounce } from "../common/util/debounce";
 import {
+  FirstWeekday,
   getHassTranslations,
   getHassTranslationsPre109,
   NumberFormat,
@@ -36,6 +37,9 @@ declare global {
     "hass-time-format-select": {
       time_format: TimeFormat;
     };
+    "hass-first-weekday-select": {
+      first_weekday: FirstWeekday;
+    };
     "translations-updated": undefined;
   }
 }
@@ -76,6 +80,9 @@ export default <T extends Constructor<HassBaseEl>>(superClass: T) =>
       this.addEventListener("hass-time-format-select", (e) => {
         this._selectTimeFormat((e as CustomEvent).detail, true);
       });
+      this.addEventListener("hass-first-weekday-select", (e) => {
+        this._selectFirstWeekday((e as CustomEvent).detail, true);
+      });
       this._loadCoreTranslations(getLocalLanguage());
     }
 
@@ -114,6 +121,13 @@ export default <T extends Constructor<HassBaseEl>>(superClass: T) =>
           // We just got time_format from backend, no need to save back
           this._selectTimeFormat(locale.time_format, false);
         }
+        if (
+          locale?.first_weekday &&
+          this.hass!.locale.first_weekday !== locale.first_weekday
+        ) {
+          // We just got first_weekday from backend, no need to save back
+          this._selectFirstWeekday(locale.first_weekday, false);
+        }
       });
 
       this.hass!.connection.subscribeEvents(
@@ -161,6 +175,18 @@ export default <T extends Constructor<HassBaseEl>>(superClass: T) =>
       }
     }
 
+    private _selectFirstWeekday(
+      first_weekday: FirstWeekday,
+      saveToBackend: boolean
+    ) {
+      this._updateHass({
+        locale: { ...this.hass!.locale, first_weekday: first_weekday },
+      });
+      if (saveToBackend) {
+        saveTranslationPreferences(this.hass!, this.hass!.locale);
+      }
+    }
+
     private _selectLanguage(language: string, saveToBackend: boolean) {
       if (!this.hass) {
         // should not happen, do it to avoid use this.hass!
diff --git a/src/translations/en.json b/src/translations/en.json
index a993014576..374c847570 100755
--- a/src/translations/en.json
+++ b/src/translations/en.json
@@ -1117,6 +1117,15 @@
       "day": "{count} {count, plural,\n  one {day}\n  other {days}\n}",
       "week": "{count} {count, plural,\n  one {week}\n  other {weeks}\n}"
     },
+    "weekdays": {
+      "monday": "Monday",
+      "tuesday": "Tuesday",
+      "wednesday": "Wednesday",
+      "thursday": "Thursday",
+      "friday": "Friday",
+      "saturday": "Saturday",
+      "sunday": "Sunday"
+    },
     "errors": {
       "config": {
         "no_type_provided": "No type provided.",
@@ -4271,6 +4280,21 @@
             "24": "24 hours"
           }
         },
+        "first_weekday": {
+          "header": "First day of the week",
+          "dropdown_label": "First day of the week",
+          "description": "Choose the starting day for calendars.",
+          "values": {
+            "language": "Auto (use language setting)",
+            "monday": "[%key:ui::weekdays::monday%]",
+            "tuesday": "[%key:ui::weekdays::tuesday%]",
+            "wednesday": "[%key:ui::weekdays::wednesday%]",
+            "thursday": "[%key:ui::weekdays::thursday%]",
+            "friday": "[%key:ui::weekdays::friday%]",
+            "saturday": "[%key:ui::weekdays::saturday%]",
+            "sunday": "[%key:ui::weekdays::sunday%]"
+          }
+        },
         "themes": {
           "header": "Theme",
           "error_no_theme": "No themes available.",
diff --git a/src/util/common-translation.ts b/src/util/common-translation.ts
index ff7793d256..aa83e23141 100644
--- a/src/util/common-translation.ts
+++ b/src/util/common-translation.ts
@@ -76,6 +76,7 @@ export async function getUserLocale(
   const language = result?.language;
   const number_format = result?.number_format;
   const time_format = result?.time_format;
+  const first_weekday = result?.first_weekday;
   if (language) {
     const availableLanguage = findAvailableLanguage(language);
     if (availableLanguage) {
@@ -83,12 +84,14 @@ export async function getUserLocale(
         language: availableLanguage,
         number_format,
         time_format,
+        first_weekday,
       };
     }
   }
   return {
     number_format,
     time_format,
+    first_weekday,
   };
 }
 
diff --git a/test/common/datetime/format_date.ts b/test/common/datetime/format_date.ts
index f81a4d1a5d..de2293719e 100644
--- a/test/common/datetime/format_date.ts
+++ b/test/common/datetime/format_date.ts
@@ -1,7 +1,11 @@
 import { assert } from "chai";
 
 import { formatDate } from "../../../src/common/datetime/format_date";
-import { NumberFormat, TimeFormat } from "../../../src/data/translation";
+import {
+  NumberFormat,
+  TimeFormat,
+  FirstWeekday,
+} from "../../../src/data/translation";
 
 describe("formatDate", () => {
   const dateObj = new Date(2017, 10, 18, 11, 12, 13, 1400);
@@ -12,6 +16,7 @@ describe("formatDate", () => {
         language: "en",
         number_format: NumberFormat.language,
         time_format: TimeFormat.language,
+        first_weekday: FirstWeekday.language,
       }),
       "November 18, 2017"
     );
diff --git a/test/common/datetime/format_date_time.ts b/test/common/datetime/format_date_time.ts
index 25e0a26a9c..a7692cbe97 100644
--- a/test/common/datetime/format_date_time.ts
+++ b/test/common/datetime/format_date_time.ts
@@ -4,7 +4,11 @@ import {
   formatDateTime,
   formatDateTimeWithSeconds,
 } from "../../../src/common/datetime/format_date_time";
-import { NumberFormat, TimeFormat } from "../../../src/data/translation";
+import {
+  NumberFormat,
+  TimeFormat,
+  FirstWeekday,
+} from "../../../src/data/translation";
 
 describe("formatDateTime", () => {
   const dateObj = new Date(2017, 10, 18, 23, 12, 13, 400);
@@ -15,6 +19,7 @@ describe("formatDateTime", () => {
         language: "en",
         number_format: NumberFormat.language,
         time_format: TimeFormat.am_pm,
+        first_weekday: FirstWeekday.language,
       }),
       "November 18, 2017 at 11:12 PM"
     );
@@ -23,6 +28,7 @@ describe("formatDateTime", () => {
         language: "en",
         number_format: NumberFormat.language,
         time_format: TimeFormat.twenty_four,
+        first_weekday: FirstWeekday.language,
       }),
       "November 18, 2017 at 23:12"
     );
@@ -38,6 +44,7 @@ describe("formatDateTimeWithSeconds", () => {
         language: "en",
         number_format: NumberFormat.language,
         time_format: TimeFormat.am_pm,
+        first_weekday: FirstWeekday.language,
       }),
       "November 18, 2017 at 11:12:13 PM"
     );
@@ -46,6 +53,7 @@ describe("formatDateTimeWithSeconds", () => {
         language: "en",
         number_format: NumberFormat.language,
         time_format: TimeFormat.twenty_four,
+        first_weekday: FirstWeekday.language,
       }),
       "November 18, 2017 at 23:12:13"
     );
diff --git a/test/common/datetime/format_time.ts b/test/common/datetime/format_time.ts
index e8cc5f63f0..0fbaafa871 100644
--- a/test/common/datetime/format_time.ts
+++ b/test/common/datetime/format_time.ts
@@ -5,7 +5,11 @@ import {
   formatTimeWithSeconds,
   formatTimeWeekday,
 } from "../../../src/common/datetime/format_time";
-import { NumberFormat, TimeFormat } from "../../../src/data/translation";
+import {
+  NumberFormat,
+  TimeFormat,
+  FirstWeekday,
+} from "../../../src/data/translation";
 
 describe("formatTime", () => {
   const dateObj = new Date(2017, 10, 18, 23, 12, 13, 1400);
@@ -16,6 +20,7 @@ describe("formatTime", () => {
         language: "en",
         number_format: NumberFormat.language,
         time_format: TimeFormat.am_pm,
+        first_weekday: FirstWeekday.language,
       }),
       "11:12 PM"
     );
@@ -24,6 +29,7 @@ describe("formatTime", () => {
         language: "en",
         number_format: NumberFormat.language,
         time_format: TimeFormat.twenty_four,
+        first_weekday: FirstWeekday.language,
       }),
       "23:12"
     );
@@ -39,6 +45,7 @@ describe("formatTimeWithSeconds", () => {
         language: "en",
         number_format: NumberFormat.language,
         time_format: TimeFormat.am_pm,
+        first_weekday: FirstWeekday.language,
       }),
       "11:12:13 PM"
     );
@@ -47,6 +54,7 @@ describe("formatTimeWithSeconds", () => {
         language: "en",
         number_format: NumberFormat.language,
         time_format: TimeFormat.twenty_four,
+        first_weekday: FirstWeekday.language,
       }),
       "23:12:13"
     );
@@ -62,6 +70,7 @@ describe("formatTimeWeekday", () => {
         language: "en",
         number_format: NumberFormat.language,
         time_format: TimeFormat.am_pm,
+        first_weekday: FirstWeekday.language,
       }),
       "Wednesday 11:12 PM"
     );
@@ -70,6 +79,7 @@ describe("formatTimeWeekday", () => {
         language: "en",
         number_format: NumberFormat.language,
         time_format: TimeFormat.twenty_four,
+        first_weekday: FirstWeekday.language,
       }),
       "Wednesday 23:12"
     );
diff --git a/test/common/datetime/relative_time.ts b/test/common/datetime/relative_time.ts
index 2e020e1ddc..b91a0bef92 100644
--- a/test/common/datetime/relative_time.ts
+++ b/test/common/datetime/relative_time.ts
@@ -1,13 +1,18 @@
 import { assert } from "chai";
 
 import { relativeTime } from "../../../src/common/datetime/relative_time";
-import { NumberFormat, TimeFormat } from "../../../src/data/translation";
+import {
+  NumberFormat,
+  TimeFormat,
+  FirstWeekday,
+} from "../../../src/data/translation";
 
 describe("relativeTime", () => {
   const locale = {
     language: "en",
     number_format: NumberFormat.language,
     time_format: TimeFormat.language,
+    first_weekday: FirstWeekday.language,
   };
 
   it("now", () => {
diff --git a/test/common/entity/compute_state_display.ts b/test/common/entity/compute_state_display.ts
index 4d9e2cca67..095be174f4 100644
--- a/test/common/entity/compute_state_display.ts
+++ b/test/common/entity/compute_state_display.ts
@@ -5,6 +5,7 @@ import {
   FrontendLocaleData,
   NumberFormat,
   TimeFormat,
+  FirstWeekday,
 } from "../../../src/data/translation";
 
 let localeData: FrontendLocaleData;
@@ -19,6 +20,7 @@ describe("computeStateDisplay", () => {
       language: "en",
       number_format: NumberFormat.comma_decimal,
       time_format: TimeFormat.am_pm,
+      first_weekday: FirstWeekday.language,
     };
   });
 
diff --git a/test/common/string/format_number.ts b/test/common/string/format_number.ts
index d9e6109cb5..f762f22305 100644
--- a/test/common/string/format_number.ts
+++ b/test/common/string/format_number.ts
@@ -5,6 +5,7 @@ import {
   FrontendLocaleData,
   NumberFormat,
   TimeFormat,
+  FirstWeekday,
 } from "../../../src/data/translation";
 
 describe("formatNumber", () => {
@@ -13,6 +14,7 @@ describe("formatNumber", () => {
     language: "en",
     number_format: NumberFormat.language,
     time_format: TimeFormat.language,
+    first_weekday: FirstWeekday.language,
   };
 
   // Node only ships with English support for `Intl`, so we can not test for other number formats here.
diff --git a/yarn.lock b/yarn.lock
index 5b3051dcaf..316610220e 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -9145,6 +9145,7 @@ fsevents@^1.2.7:
     webpack-dev-server: ^4.3.0
     webpack-manifest-plugin: ^4.0.2
     webpackbar: ^5.0.0-3
+    weekstart: ^1.1.0
     workbox-build: ^6.4.2
     workbox-cacheable-response: ^6.4.2
     workbox-core: ^6.4.2
@@ -15781,6 +15782,13 @@ typescript@^4.4.3:
   languageName: node
   linkType: hard
 
+"weekstart@npm:^1.1.0":
+  version: 1.1.0
+  resolution: "weekstart@npm:1.1.0"
+  checksum: afce96e0b95809a30f00fa02b13a0927324d9f76b9c10ce6b3de9bbd5926615156f8a0526c63e2bd1cabdc8ec3da68b8df8d6608b6364ded11b5da300a8cfcb4
+  languageName: node
+  linkType: hard
+
 "whatwg-url@npm:^7.0.0":
   version: 7.1.0
   resolution: "whatwg-url@npm:7.1.0"