Internationalization: Change locale preference to language (#58359)

* backend locale -> language

* frontend locale -> language

* sample.ini and tests

* fix few last locale -> language

* fix few last locale -> language

pkg/api/index.go

@@ -45,15 +45,17 @@ func (hs *HTTPServer) setIndexViewData(c *models.ReqContext) (*dtos.IndexViewDat
 		return nil, err
 	}
 
-	// Set locale to the preference, otherwise fall back to the accept language header.
-	// In practice, because the preference has configuration-backed default, the header
-	// shouldn't frequently be used
+	// 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"
+	language := "" // frontend will set the default language
 
-	if hs.Features.IsEnabled(featuremgmt.FlagInternationalization) && prefs.JSONData.Locale != "" {
-		locale = prefs.JSONData.Locale
-	} else if len(acceptLangHeader) > 0 {
+	if hs.Features.IsEnabled(featuremgmt.FlagInternationalization) && prefs.JSONData.Language != "" {
+		language = prefs.JSONData.Language
+	}
+
+	if len(acceptLangHeader) > 0 {
 		parts := strings.Split(acceptLangHeader, ",")
 		locale = parts[0]
 	}
@@ -100,6 +102,7 @@ func (hs *HTTPServer) setIndexViewData(c *models.ReqContext) (*dtos.IndexViewDat
 			Timezone:                   prefs.Timezone,
 			WeekStart:                  weekStart,
 			Locale:                     locale,
+			Language:                   language,
 			HelpFlags1:                 c.HelpFlags1,
 			HasEditPermissionInFolders: hasEditPerm,
 		},