English Translation
I’m glad you’re enjoying it.
Please explain what it wouldn’t be me alegro que
I’d say that both work and both are common.
Being a pedant, I would suggest “me alegro de que”. 
1 Like
As I understand it, the difference between me alegra que … and me alegro de que is what or who is the agent, the thing acting, in the phrase. In the first case, you’re saying “It makes me happy …” - the agent is it (e.g. news that your favourite team has won their last match) not you. In the second case, you’re saying "I’m happy … ". Here you are the agent. In the first case stuff is happening to you, in the second, you’re owning the experience.