diff --git a/apps/client/src/widgets/collections/calendar/index.tsx b/apps/client/src/widgets/collections/calendar/index.tsx
index 3aa9fc1d6..c22155585 100644
--- a/apps/client/src/widgets/collections/calendar/index.tsx
+++ b/apps/client/src/widgets/collections/calendar/index.tsx
@@ -74,7 +74,8 @@ export const LOCALE_MAPPINGS: Record<LOCALE_IDS, (() => Promise<{ default: Local
     pt: () => import("@fullcalendar/core/locales/pt"),
     "pt_br": () => import("@fullcalendar/core/locales/pt-br"),
     uk: () => import("@fullcalendar/core/locales/uk"),
-    en: null
+    en: null,
+    "en_rtl": null,
 };
 
 export default function CalendarView({ note, noteIds }: ViewModeProps<CalendarViewData>) {
diff --git a/apps/server/src/services/i18n.ts b/apps/server/src/services/i18n.ts
index 1f1db1ac6..1199bd796 100644
--- a/apps/server/src/services/i18n.ts
+++ b/apps/server/src/services/i18n.ts
@@ -12,6 +12,7 @@ export const DAYJS_LOADER: Record<LOCALE_IDS, () => Promise<typeof import("dayjs
     "cn": () => import("dayjs/locale/zh-cn.js"),
     "de": () => import("dayjs/locale/de.js"),
     "en": () => import("dayjs/locale/en.js"),
+    "en_rtl": () => import("dayjs/locale/en.js"),
     "es": () => import("dayjs/locale/es.js"),
     "fa": () => import("dayjs/locale/fa.js"),
     "fr": () => import("dayjs/locale/fr.js"),
diff --git a/packages/commons/src/lib/i18n.ts b/packages/commons/src/lib/i18n.ts
index 5970d2ab8..a6679f542 100644
--- a/packages/commons/src/lib/i18n.ts
+++ b/packages/commons/src/lib/i18n.ts
@@ -23,6 +23,13 @@ const UNSORTED_LOCALES: Locale[] = [
     { id: "tw", name: "繁體中文", electronLocale: "zh_TW" },
     { id: "uk", name: "Українська", electronLocale: "uk" },
 
+    /**
+     * Development-only languages.
+     *
+     * These are only displayed while in dev mode, to test some language particularities (such as RTL) more easily.
+     */
+    { id: "en_rtl", name: "English (right-to-left) [dev]", electronLocale: "en", rtl: true },
+
     /*
      * Right to left languages
      *