deficient

+ deficient (noun) (m / f)

GDLC:
deficient mental (o simplement deficient) adj i m i f PSIQ /DR Disminuït, totalment o parcialment, en la seva activitat intel- lectual.

I guess we could say 'mental deficient' in English but I'm not convinced that it is politically correct. Perhaps 'mentally handicapped person'? Mentally retarded and mentally challenged both seem wrong.

Also, a Google search provides us with examples of 'deficient' as a noun referring to people with other limitations (deficients visuals - partially-sighted people? and deficients auditius - the hard of hearing??)

Up until yesterday the current PC term for 'deficient mental' in BrE was "person with learning difficulties", pl: "people with learning difficulties" ; 'deficiència mental' : "learning difficulties". Yesterday my wife, who is a clinical psychologist, was reading some official document whenre the preferred term was "intellectual disability". The PC euphemisms in this field have a life of around 10 years (and of course are unlikley to be the same across the English speaking world). In BrE 'mentally deficient' was OK in the 1950s but not PC subsequently.