[Blueprints] setSiteLanguage step sets a non-persistent constants #2700
Description
Studio uses setSiteLanguage step to, well, set the site language. The language setting, however, is gone after restarting the site. This is because the language is set using await playground.defineConstant('WPLANG', language); which only affects the constants.json file, not any persistent site-related file. It seems like it would be more practical to set the wplang site option instead of a constant.