It seems like a lot of people feel an urge to take sides and say "how could Unbabel do this, it's their fault" or "how could you not read the contract, it's your fault," and I don't see any comments really discussing the underlying issues in this situation. I'm seeing a lot of fault on both sides, and lessons both sides need to learn.
Andreas, some people here have called you naive, and I have to say that on the surface I can very much see why. A decent financial incentive was enough to get you to wholly uproot your (relatively unstable) life for a group of people you had never met living in a place where you didn't speak the language and didn't know the laws. It does read, in your posts, as if you never considered the possibility that you could get screwed by these people.
I feel like part of the reason you are so upset now might be because you didn't consider possible negative outcomes. Nobody likes to be surprised. It's also reasonable to say that being defensive when people ask about your financial situation and the circumstances of this event (as you have been in comments, and in the tone this post takes), and you tell them it's none of their business, that's not fair: You made it their business when you posted it publicly online and invited comments on HN.
However, let's look at Unbabel's conduct as well: They knew who Andreas was. He's indicated they knew his situation (and I believe, from his statements and theirs, that he is telling the truth, if colored by his feelings). They knew he didn't speak Portguese, they obviously had to be aware he was willing to take the (in my opinion, fairly significant) step of moving across the continent to their country anyway, and given how quickly they fired him it seems like they knew pretty quickly after he joined that he wasn't working out. It seems like Unbabel understood that Andreas was taking large risks, and didn't try to point that out to him. Apparently, they didn't consider how it would affect his working with them until after he'd been hired.
No, they didn't HAVE to, but if they cared at all about his well-being, I think they should have considered his issues and perspective in both the hiring and the firing. He didn't enter this situation angry, and he didn't have to leave it that way. If they had given him a little more time and consideration, he wouldn't have been kicked out of his apartment and these blog posts wouldn't exist. Now, maybe Andreas didn't express to them that he would have liked that until after it was too late (but it seems like they're also refusing to speak to him at all, which just doesn't make sense to me). But it's not his responsibility to ask: Unbabel played on his naivete (whether they knew it or not) to hire him, and they were the ones who decided the relationship hadn't worked out. Their conduct was legal, but it wasn't right, and it wasn't smart.
This has gotten quite long, so I'll try to sum up: Your employers/employees are people. They don't know everything that's going on and you don't fully understand their situation no matter how much you think you know. What they present is not always what they are. If you are an employee (and your financial/skillset situation allows it), you owe it to yourself to get protection from this by understanding and negotiating your contract and by maintaining open lines of communication with your superiors, monitoring for issues (which Andreas may have done, I don't know). If you are an employer, you need to take your employees' situation into account even when you're about to fire them, and you need to be as clear and kind as you can be. Yeah, there might be more costs - they should be considered part of the cost of hiring. A disgruntled fired employee is way worse than a fired employee who cost you a month of his rent.
So, TL;DR: Be human even if you're representing a faceless corporation, or at least try to pretend you are. This situation happened because nobody was communicating and nobody was thinking about what the other guy was thinking about. It could easily have been avoided with a little more world-wariness and a little more generosity.