The press release in English translation:
The Grand Duke and the Grand Duchess are pleased to announce, together with Prince Félix and Princess Claire, that the name of their grandson is His Royal Highness Prince Liam Henri Hartmut of Nassau.Prince Liam, who was born in Geneva on 28 November 2016, is the second child of Prince Félix and Princess Claire of Luxembourg. It is easy to guess that the second name Henri is after Liam's grandfather Grand Duke Henri, and the third name Hartmut after Princess Claire's father Hartmut Lademacher.
Liam is an Irish short form of Uilliam, a derivative of William, Wilhelm (Willahelm) and Guillaume. As both Prince Liam's uncle and grand uncle have the name Guilluame, I guess Liam is a sensible way of not creating too much confusion. I suppose that the name in French is pronounced differently than in English.