[MM-60792] Add support for loading experimental (e.g., in progress) languages (#29009)

* Add support for loading experimental (e.g., in progress) languages

* Fix e2e config

* Improve language labels

* Improvements

server/config/client.go

@@ -75,6 +75,8 @@ func GenerateClientConfig(c *model.Config, telemetryID string, license *model.Li
 	props["EnablePublicLink"] = strconv.FormatBool(*c.FileSettings.EnablePublicLink)
 
 	props["AvailableLocales"] = *c.LocalizationSettings.AvailableLocales
+	props["EnableExperimentalLocales"] = strconv.FormatBool(*c.LocalizationSettings.EnableExperimentalLocales)
+
 	props["SQLDriverName"] = *c.SqlSettings.DriverName
 
 	props["EnableEmojiPicker"] = strconv.FormatBool(*c.ServiceSettings.EnableEmojiPicker)

server/public/model/config.go

@@ -2597,9 +2597,10 @@ func (s *ComplianceSettings) SetDefaults() {
 }
 
 type LocalizationSettings struct {
-	DefaultServerLocale *string `access:"site_localization"`
-	DefaultClientLocale *string `access:"site_localization"`
-	AvailableLocales    *string `access:"site_localization"`
+	DefaultServerLocale       *string `access:"site_localization"`
+	DefaultClientLocale       *string `access:"site_localization"`
+	AvailableLocales          *string `access:"site_localization"`
+	EnableExperimentalLocales *bool   `access:"site_localization"`
 }
 
 func (s *LocalizationSettings) SetDefaults() {
@@ -2614,6 +2615,10 @@ func (s *LocalizationSettings) SetDefaults() {
 	if s.AvailableLocales == nil {
 		s.AvailableLocales = NewPointer("")
 	}
+
+	if s.EnableExperimentalLocales == nil {
+		s.EnableExperimentalLocales = NewPointer(false)
+	}
 }
 
 type SamlSettings struct {