diff --git a/packages/grafana-data/src/types/config.ts b/packages/grafana-data/src/types/config.ts
index 2426ed3338c..dbfbc5eeeb3 100644
--- a/packages/grafana-data/src/types/config.ts
+++ b/packages/grafana-data/src/types/config.ts
@@ -246,6 +246,7 @@ export interface GrafanaConfig {
    * Grafana's supported language.
    */
   language: string | undefined;
+  locale: string;
 }
 
 export interface SqlConnectionLimits {
diff --git a/packages/grafana-runtime/src/config.ts b/packages/grafana-runtime/src/config.ts
index e6444cdb80c..8b0beab714f 100644
--- a/packages/grafana-runtime/src/config.ts
+++ b/packages/grafana-runtime/src/config.ts
@@ -208,6 +208,12 @@ export class GrafanaBootConfig implements GrafanaConfig {
    */
   language: string | undefined;
 
+  /**
+   * Locale used in Grafana's UI. Default to 'es-US' in the backend and overwritten when the user select a different one in SharedPreferences.
+   * This is the locale that is used for date formatting and other locale-specific features.
+   */
+  locale: string;
+
   constructor(options: GrafanaBootConfig) {
     this.bootData = options.bootData;
 
@@ -243,6 +249,8 @@ export class GrafanaBootConfig implements GrafanaConfig {
     this.theme2 = getThemeById(this.bootData.user.theme);
     this.bootData.user.lightTheme = this.theme2.isLight;
     this.theme = this.theme2.v1;
+
+    this.locale = options.bootData.user.locale;
   }
   geomapDefaultBaseLayer?: MapLayerOptions<any> | undefined;
   listDashboardScopesEndpoint?: string | undefined;
diff --git a/pkg/api/index.go b/pkg/api/index.go
index 68423b8d0f8..016a78366c6 100644
--- a/pkg/api/index.go
+++ b/pkg/api/index.go
@@ -69,7 +69,7 @@ func (hs *HTTPServer) setIndexViewData(c *contextmodel.ReqContext) (*dtos.IndexV
 	// Locale is used for some number and date/time formatting, whereas language is used just for
 	// translating words in the interface
 	acceptLangHeader := c.Req.Header.Get("Accept-Language")
-	locale := "en-US" // default to en-US formatting, but use the accept-lang header or user's preference
+	locale := "en-US" // default to en formatting, but use the accept-lang header or user's preference
 	language := ""    // frontend will set the default language
 	urlPrefs := getURLPrefs(c)
 
@@ -85,6 +85,7 @@ func (hs *HTTPServer) setIndexViewData(c *contextmodel.ReqContext) (*dtos.IndexV
 	}
 
 	if hs.Features.IsEnabled(c.Req.Context(), featuremgmt.FlagLocaleFormatPreference) {
+		locale = "en" // default to "en", not "en-US", matching the locale code
 		if urlPrefs.Locale != "" {
 			locale = urlPrefs.Locale
 		} else if prefs.JSONData.Locale != "" {
diff --git a/pkg/services/preference/prefimpl/pref_test.go b/pkg/services/preference/prefimpl/pref_test.go
index afc40f9e37f..85a859935ed 100644
--- a/pkg/services/preference/prefimpl/pref_test.go
+++ b/pkg/services/preference/prefimpl/pref_test.go
@@ -92,7 +92,7 @@ func TestGetWithDefaults_withUserAndOrgPrefs(t *testing.T) {
 			WeekStart:       &weekStartOne,
 			JSONData: &pref.PreferenceJSONData{
 				Language: "en-GB",
-				Locale:   "en-US",
+				Locale:   "en",
 			},
 		},
 		pref.Preference{
@@ -104,7 +104,7 @@ func TestGetWithDefaults_withUserAndOrgPrefs(t *testing.T) {
 			WeekStart:       &weekStartTwo,
 			JSONData: &pref.PreferenceJSONData{
 				Language: "en-AU",
-				Locale:   "es-ES",
+				Locale:   "es",
 			},
 		},
 	)
@@ -120,7 +120,7 @@ func TestGetWithDefaults_withUserAndOrgPrefs(t *testing.T) {
 			HomeDashboardID: 4,
 			JSONData: &pref.PreferenceJSONData{
 				Language: "en-AU",
-				Locale:   "es-ES",
+				Locale:   "es",
 			},
 		}
 		if diff := cmp.Diff(expected, preference); diff != "" {
@@ -140,7 +140,7 @@ func TestGetWithDefaults_withUserAndOrgPrefs(t *testing.T) {
 			HomeDashboardID: 1,
 			JSONData: &pref.PreferenceJSONData{
 				Language: "en-GB",
-				Locale:   "en-US",
+				Locale:   "en",
 			},
 		}
 		if diff := cmp.Diff(expected, preference); diff != "" {
@@ -162,7 +162,7 @@ func TestGetDefaults_JSONData(t *testing.T) {
 		Language: "en-GB",
 	}
 	orgPreferencesWithLocaleJsonData := pref.PreferenceJSONData{
-		Locale: "en-US",
+		Locale: "en",
 	}
 	team2PreferencesJsonData := pref.PreferenceJSONData{}
 	team1PreferencesJsonData := pref.PreferenceJSONData{}
@@ -248,7 +248,7 @@ func TestGetDefaults_JSONData(t *testing.T) {
 		require.Equal(t, &pref.Preference{
 			WeekStart: &weekStart,
 			JSONData: &pref.PreferenceJSONData{
-				Locale:       "en-US",
+				Locale:       "en",
 				QueryHistory: queryPreference,
 			},
 		}, preference)
diff --git a/public/app/app.ts b/public/app/app.ts
index ef7460001e7..647124ce8dc 100644
--- a/public/app/app.ts
+++ b/public/app/app.ts
@@ -135,7 +135,7 @@ export class GrafanaApp {
       // This needs to be done after the `initEchoSrv` since it is being used under the hood.
       startMeasure('frontend_app_init');
 
-      setLocale(config.bootData.user.locale);
+      setLocale(config.locale);
       setWeekStart(config.bootData.user.weekStart);
       setPanelRenderer(PanelRenderer);
       setPluginPage(PluginPage);
diff --git a/public/app/core/internationalization/dates.ts b/public/app/core/internationalization/dates.ts
index 8f0aaa14d7c..bdadd9ba863 100644
--- a/public/app/core/internationalization/dates.ts
+++ b/public/app/core/internationalization/dates.ts
@@ -2,16 +2,16 @@ import '@formatjs/intl-durationformat/polyfill';
 import deepEqual from 'fast-deep-equal';
 import memoize from 'micro-memoize';
 
-import { getI18next } from './index';
+import { config } from 'app/core/config';
 
 const deepMemoize: typeof memoize = (fn) => memoize(fn, { isEqual: deepEqual });
 
-const createDateTimeFormatter = deepMemoize((language: string, options: Intl.DateTimeFormatOptions) => {
-  return new Intl.DateTimeFormat(language, options);
+const createDateTimeFormatter = deepMemoize((locale: string, options: Intl.DateTimeFormatOptions) => {
+  return new Intl.DateTimeFormat(locale, options);
 });
 
-const createDurationFormatter = deepMemoize((language: string, options: Intl.DurationFormatOptions) => {
-  return new Intl.DurationFormat(language, options);
+const createDurationFormatter = deepMemoize((locale: string, options: Intl.DurationFormatOptions) => {
+  return new Intl.DurationFormat(locale, options);
 });
 
 export const formatDate = deepMemoize(
@@ -20,17 +20,17 @@ export const formatDate = deepMemoize(
       return formatDate(new Date(value), format);
     }
 
-    const i18n = getI18next();
-    const dateFormatter = createDateTimeFormatter(i18n.language, format);
+    const locale = config.locale;
+    const dateFormatter = createDateTimeFormatter(locale, format);
     return dateFormatter.format(value);
   }
 );
 
 export const formatDuration = deepMemoize(
   (duration: Intl.DurationInput, options: Intl.DurationFormatOptions = {}): string => {
-    const i18n = getI18next();
+    const locale = config.locale;
 
-    const dateFormatter = createDurationFormatter(i18n.language, options);
+    const dateFormatter = createDurationFormatter(locale, options);
     return dateFormatter.format(duration);
   }
 );