Hi,
Yes I can confirm that Translator API returns translated tests in same order as input. Try this example:
curl -X POST "https://api.cognitive.microsofttranslator.com/translate?api-version=3.0&from=en&to=en" -H "Ocp-Apim-Subscription-Key: <**your-key**>"-H "Ocp-Apim-Subscription-Region: <**your-region**>" -H "Content-Type: application/json; charset=UTF-8" -d "[{'Text':'Hey there?'}, {'Text': 'How is your day going?'}, {'Text': 'I am fine, thank you.'}]"