i18n: Update internationalization/dates.ts to use locale (#103731)

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 != "" {