The letter is "Against Censorship and Its Academic Supporters", if one finds censorship objectionable then it is reasonable to object to censorship even when the censorship is legal. If the law is not being applied correctly then it is objectionable in every way. It is highly likely X/Twitter's behaviour in Brazil is intended to comply with the law and is guided by professionals rather than "amateurs", although I have to say the idea that citizens cannot know what laws mean is completely absurd and obviously disproved by people obeying them.

The letter is written by Luciano de Castro, I know nothing about him but I have a gut feeling that somehow he might know what this "foreign language" law means and the context around it.