"Mereka tidak resmi."
Terjemahan:They are not official.
Legal is not the same than official in English.
Legal: allowed by the law /connected with the law: (Contoh: legal advice, legal obligation, legal status, legal right, legal action, the legal representatives (=lawyers)
Is alcohol legal in your country?
relating to a position of responsibility:
He visited China in his official capacity as America's trade representative.
the official photos of the president's tour of India T he Queen will attend the official opening of the theatre in June.
There is to be an official inquiry into the incident.
If a piece of information is official, it has been announced publicly with authority.
Resmi = official.
Legal = legal, or sah (depending the context)
Legal sudah diserap dalam bahasa indonesia, seperti radio.
In other words, duolingo want use the right word
I'm the head of know you, because legal in the sense of the indonesian language is sah, while official is resmi, please thinking