Export fallback language tag ("en") as a constant

src/bin/shared/constants.ts

@@ -67,3 +67,5 @@ export type LoginThemePageId = (typeof loginThemePageIds)[number];
 export type AccountThemePageId = (typeof accountThemePageIds)[number];
 
 export const containerName = "keycloak-keycloakify";
+
+export const fallbackLanguageTag = "en";