This plugin works as an add-on for Loco Translate official plugin. First, you need to install and activate the free version of “Loco Translate” then install this addon and use one-click machine translations (supported by Yandex Translate and Deepl Translator).
No, there is no requirement for any translate API key to use this plugin free or pro version. It uses free page translation widgets and services for unlimited automatic translations.
Free license users can use Yandex Translate Widget but if you are using a premium license then you can also use Google Translate Widget and DeepL Doc Translator.
Google Translate and Yandex Translate support translation between many languages that support over 100 languages including English, Spanish, French, Chinese (Simplified and Traditional), Japanese, Arabic, Russian, Hindi, and Bengali, with the list subject to change over time.