Simplify the following text for a Grade 9 native English-speaking person.
Original: The ancient Thracians were a group of Indo-European tribes inhabiting areas in Southeastern Europe . They spoke the Thracian language â `` a scarcely attested branch of the Indo-European language family .
Simplified: The ancient Thracians were a group of Indo-European tribes who spoke the Thracian language - a rare branch of the Indo-European language family .