diff --git a/apps/client/src/widgets/collections/calendar/index.tsx b/apps/client/src/widgets/collections/calendar/index.tsx
index bac6862b2..8bf5ce7f9 100644
--- a/apps/client/src/widgets/collections/calendar/index.tsx
+++ b/apps/client/src/widgets/collections/calendar/index.tsx
@@ -77,6 +77,7 @@ export const LOCALE_MAPPINGS: Record<DISPLAYABLE_LOCALE_IDS, (() => Promise<{ de
     "pt_br": () => import("@fullcalendar/core/locales/pt-br"),
     uk: () => import("@fullcalendar/core/locales/uk"),
     en: null,
+    "en-GB": () => import("@fullcalendar/core/locales/en-gb"),
     "en_rtl": null,
     ar: () => import("@fullcalendar/core/locales/ar")
 };
diff --git a/apps/client/src/widgets/type_widgets/MindMap.tsx b/apps/client/src/widgets/type_widgets/MindMap.tsx
index eb54170c3..f8409c75c 100644
--- a/apps/client/src/widgets/type_widgets/MindMap.tsx
+++ b/apps/client/src/widgets/type_widgets/MindMap.tsx
@@ -28,6 +28,7 @@ const LOCALE_MAPPINGS: Record<DISPLAYABLE_LOCALE_IDS, Options["locale"] | null>
     de: null,
     en: "en",
     en_rtl: "en",
+    "en-GB": "en",
     es: "es",
     fr: "fr",
     it: "it",
diff --git a/apps/client/src/widgets/type_widgets/canvas/i18n.spec.ts b/apps/client/src/widgets/type_widgets/canvas/i18n.spec.ts
index 71eb3d18c..c77e4979d 100644
--- a/apps/client/src/widgets/type_widgets/canvas/i18n.spec.ts
+++ b/apps/client/src/widgets/type_widgets/canvas/i18n.spec.ts
@@ -22,6 +22,7 @@ describe("Canvas i18n", () => {
             if (locale.contentOnly || locale.devOnly) continue;
             const languageCode = LANGUAGE_MAPPINGS[locale.id];
             if (!supportedLanguageCodes.has(languageCode)) {
+                console.log("Supported locales:", Array.from(supportedLanguageCodes.values()).join(", "));
                 expect.fail(`Unable to find locale for ${locale.id} -> ${languageCode}.`)
             }
         }
diff --git a/apps/client/src/widgets/type_widgets/canvas/i18n.ts b/apps/client/src/widgets/type_widgets/canvas/i18n.ts
index 43ee724cf..47324abfc 100644
--- a/apps/client/src/widgets/type_widgets/canvas/i18n.ts
+++ b/apps/client/src/widgets/type_widgets/canvas/i18n.ts
@@ -1,10 +1,12 @@
+import { Language } from "@excalidraw/excalidraw/i18n";
 import type { DISPLAYABLE_LOCALE_IDS } from "@triliumnext/commons";
 
-export const LANGUAGE_MAPPINGS: Record<DISPLAYABLE_LOCALE_IDS, string | null> = {
+export const LANGUAGE_MAPPINGS: Record<DISPLAYABLE_LOCALE_IDS, Language["code"] | null> = {
     ar: "ar-SA",
     cn: "zh-CN",
     de: "de-DE",
     en: "en",
+    "en-GB": "en",
     en_rtl: "en",
     es: "es-ES",
     fr: "fr-FR",
diff --git a/apps/server/src/services/i18n.ts b/apps/server/src/services/i18n.ts
index be7ebdeb5..82eb6f408 100644
--- a/apps/server/src/services/i18n.ts
+++ b/apps/server/src/services/i18n.ts
@@ -7,11 +7,13 @@ import hidden_subtree from "./hidden_subtree.js";
 import { LOCALES, type Locale, type LOCALE_IDS } from "@triliumnext/commons";
 import dayjs, { Dayjs } from "dayjs";
 
+// When adding a new locale, prefer the version with hyphen instead of underscore.
 export const DAYJS_LOADER: Record<LOCALE_IDS, () => Promise<typeof import("dayjs/locale/en.js")>> = {
     "ar": () => import("dayjs/locale/ar.js"),
     "cn": () => import("dayjs/locale/zh-cn.js"),
     "de": () => import("dayjs/locale/de.js"),
     "en": () => import("dayjs/locale/en.js"),
+    "en-GB": () => import("dayjs/locale/en-gb.js"),
     "en_rtl": () => import("dayjs/locale/en.js"),
     "es": () => import("dayjs/locale/es.js"),
     "fa": () => import("dayjs/locale/fa.js"),
diff --git a/packages/ckeditor5/src/i18n.ts b/packages/ckeditor5/src/i18n.ts
index 3053f4b7d..a409fa437 100644
--- a/packages/ckeditor5/src/i18n.ts
+++ b/packages/ckeditor5/src/i18n.ts
@@ -10,6 +10,11 @@ interface LocaleMapping {
 const LOCALE_MAPPINGS: Record<DISPLAYABLE_LOCALE_IDS, LocaleMapping | null> = {
     en: null,
     en_rtl: null,
+    "en-GB": {
+        languageCode: "en-GB",
+        coreTranslation: () => import("ckeditor5/translations/en-gb.js"),
+        premiumFeaturesTranslation: () => import("ckeditor5-premium-features/translations/en-gb.js"),
+    },
     ar: {
         languageCode: "ar",
         coreTranslation: () => import("ckeditor5/translations/ar.js"),
diff --git a/packages/commons/src/lib/i18n.ts b/packages/commons/src/lib/i18n.ts
index 65ff196d2..8d2bc0232 100644
--- a/packages/commons/src/lib/i18n.ts
+++ b/packages/commons/src/lib/i18n.ts
@@ -15,6 +15,7 @@ const UNSORTED_LOCALES = [
     { id: "cn", name: "简体中文", electronLocale: "zh_CN" },
     { id: "de", name: "Deutsch", electronLocale: "de" },
     { id: "en", name: "English", electronLocale: "en" },
+    { id: "en-GB", name: "English (United Kingdom)", electronLocale: "en_GB" },
     { id: "es", name: "Español", electronLocale: "es" },
     { id: "fr", name: "Français", electronLocale: "fr" },
     { id: "it", name: "Italiano", electronLocale: "it" },