Possible Clues:

• Ancient Iranian language
• Thus spake Zarathustra
• Zend, language of the Iranian branch of the Indo-European family
• A top article in ancient language
• Savant troubled about English language that's passed out of use
• Two articles about underwear in sacred text
• Articles holding underwear, in an Iranian language
• Is French in a leading position? It's a language that's faded!
• Language in a match, last of season
• A language of Iranian branch of the Indo-European family, also known as Zend