en and simple are practically same for MT engines and they throw errors lile
{"status":500,"type":"internal_error","title":"Error","detail":"Translation with Google failed for en > en. Error: 400 : Bad language pair: en|en","method":"POST","uri":"/v2/translate/en/simple/Google"}
Listing Google, Yandex as MT services available for the language pair is confusing too. So remove the MT engine options for en->simple or simple->en language pairs