Samus Aran suffered from elective mutism for almost the entirety of her teenage years, the disorder being notably more severe during her earliest years as a part of the galactic federation police force. This disorder was brought on by several factors, but most notably was the fact that prior to joining the GF, she didn’t speak much English/Galactic Standard to begin with. The Chozo initially found communicating with Samus to be extremely difficult; given that the Chozo are a raptor-like species of humanoids, their language is defined by sounds that to a stranger’s ear would be described as ‘bird-like:’ trills, screeches, melodies and whistles of various forms instead of familiar constant noises of human tongues ( their beaks are not as flexible as our lips. ) As a result, there was a period where communication had to be relayed through Mother Brain, who acted as translator. Initially, Samus had difficulty picking up the complex nuances of the verbal Chozo language but picked up sign language well enough where she could converse without Mother Brain having to act as a proxy, so sign language developed into her main method of communication. This, combined with the severe isolation that came from growing up around no more than a handful of other sentient organisms, led to Samus being nearly mute before she left home.
Between her lack of socialization, the vast culture shock of being exposed to galactic civilization, and her own dysphoria with being recognized as and treated as human despite identifying with her adoptive alien culture, in the first years of training at the galactic federation Samus abandoned vocalization almost altogether, and she was diagnosed by a federation psychologist as suffering from elective mutism, an anxiety disorder. That is not to say Samus didn’t communicate verbally in at least some form, verbally, but she was reduced to sharp whistles or hisses for the sake of pulling attention, or other involuntary responses she had picked up via osmosis from growing up with the Chozo. At first, she reacted extremely negatively to suggestions for treatment and therapy, but as time progressed and she began to adjust to her new surroundings ( and they began to adjust to her ), she eventually began to speak again with the help of her new friends and comrades.
Currently, Samus is able to speak a plethora of languages with ease and carries little evidence of the anxiety of her youth. She does not, however, speak unless it is necessary, i.e. in conversation with another, as she naturally prefers non-verbal communication. She can go for months or even years comfortably silent, barely uttering a word to anyone, and once given the indication that verbal communication isn’t necessary she’ll drop it completely. In her powersuit, her inability to sign fully ( with the arm cannon ) is circumvented by the suit’s ability to pick up mental commands and verbalize her words without her having to actually speak.
