The process was quite dynamic and for me personally long and demanding. It lasted 3 months, and I visited Bloomberg offices in London 4 times. But it was one of the best experiences in my life so far.
I had a phone interview of 45 minutes, then 3 face to face interviews and a language test over the phone (talking & email writing).
I have studied everything, from detailed understanding of companies products and practices, current affairs that I have tried to understand in depth (that really gave me a huge advantage) and out of the box thinking about the future challenges. On top I have been revising literally all theory about Financial Markets and watched Khan Academy youtube videos about swaps, mortages, CDOs... (guy that made videos is a GOD).
The key was to constantly follow markets, and by constantly I mean every hour, like that you can enter the world of BBG faster and once you match that with Bloomberg products and culture it is a bingo.
Finally Glassadoor previous interview entries are of fundamental purpose! I have extracted all questions and wrote in advance answers, and updated them as I went through each interview.
About the interviews, they are demanding, but they wow you. The extent to which they challenge to use your brain is really something. I received questions like : scenario based (CEO calls you, analyst calls you - who will you answer first - they told me there is no right answer, they just want to see how you work though dilemma); direct questions: why BBG, why not investment bank (expect this question in every interview), what are challenges & opportunities, explain to a kid share and a bond, sell me the tickets for the musical in London, explain me how ECB aims to increase inflation by employing QE and lower interest rates (step by step - I used here all macroeconomic theory and it went good), how do you calculate inflation (CPI) and what went wrong if the inflation is not correct on terminal...
My personal advice, even when you do not know the question (I did not know many I have to admit), do not say I DO NOT KNOW, just simply say "That was not my focus, can you tell me so I learn more on that topic." Because that is the truth, we came to learn. Just be comfortable with yourself and logically work through a problem or a question. They want to put you in a hot seat, just remain calm and breathe.