The initial interview requires you to speak in complete english, any other language is not allowed. It is quite easy, they will ask you to introduce yourself, and will ask you follow up questions so the conversation can keep going. I think it's all about fluency and coherence. The final interview is harder, they will still ask you to introduce yourself, but there will be technical questions after regarding their telecommunication and their company. The interviewers I encountered are all kind and friendly.