Run only english on staging (#16992)

* Run only english on staging

* Revert "Run only english on staging"

This reverts commit af34c7a4497db4867a6f3facd34af316cd6b4b9a.

* Update app.json

* Update app.json

Co-authored-by: Chiedo John <2156688+chiedo@users.noreply.github.com>

Author: heiskr

app.json

@@ -2,7 +2,8 @@
   "name": "docs.github.com",
   "env": {
     "NODE_ENV": "production",
-    "NPM_CONFIG_PRODUCTION": "true"
+    "NPM_CONFIG_PRODUCTION": "true",
+    "ENABLED_LANGUAGES": "en, de"
   },
   "buildpacks": [
     { "url": "https://github.com/DataDog/heroku-buildpack-datadog.git#1.21" },