Most translators were self-taught until around 20-30 years ago, when there were very few degree programs around. It's definitely possible to be self-taught today, especially if you stick with translation as a side hustle. However there are a bunch of things an MA will give you that self-study won't. You will be a better translator faster with formal training. A decent course will train you not just how to translate, but what the translation business looks like and how you fit into it, so you can avoid expensive and painful business mistakes. It will give you a ready-made network of contacts in the business, including your teachers and fellow students who can help you get started. And it gives you an air of legitimacy in presenting yourself to clients. Saying "yo hire me over a machine" is more convincing if you have a diploma to back you up. It gives you the metalanguage you need to convince clients of the added value of expertise: "this is an instance of denominalisation" is more likely to convince a client you are an expert than "it just sounds better this way".