By default the comparison tool displays 3 translation providers lined up in alphabetical order (Google Translate, Microsoft Translator, Translator). The forth translator, Yandex, is hidden due to the lack of space.
If you want to change the provider, or change the order of the translators, use the "Replace with" icon, then click on the provider.
The selected translation provider will be interchanged with the new provider.
If some of the providers don't support a chosen language, the number of translation windows may change to two, or the provider may be interchanged to a supported provider.