Complete the extra-information clause with a four-word fragment: Omar, ___, offered to translate the notice. Use who followed by the simple-present verb speaks and the phrase four languages, with no modal or added words.
Richtige Antwort
who speaks four languages
Erklärung
Who refers to Omar and supplies the subject of speaks inside the non-defining clause. That would be the closest competing form in some defining contexts, but it is not allowed in this comma-set construction.