What is 'I'm Portuguese' in Portuguese?
'Sou português' if the speaker is male, or 'Sou portuguesa', if the speaker is female, may be Portuguese equivalents of 'I'm Portuguese'.
The verb 'sou' means '[I] am'. The subject pronoun 'eu' ['I'] doesn't have to be used since the subject is clear from the verb form. The masculine adjective 'português' and the feminine adjective 'portuguesa' mean 'Portuguese'.