the whole process is in English. They even stress it out that nobody can speak any other languages, especially during group discussions.
About checking how well you can speak your third language-if one of them speaks the same language as you do maybe they can check. Otherwise it is impossible, I guess. They will write down only the languages you can speak fluently, for the time being they have to trust you on that, maybe they will test you later on in Dubai.
Good luck