The most common and most likely answer to this crossword clue is the 4 letter word GEEZ
G
E
E
Z
More clues leading to the result GEEZ
Buddy explains!

The straight part
We know that "ancient language" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ancient language = geez.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GEEZ mean?
GEEZ interjection- An exclamation denoting surprise or frustration.
- Informal address to a male.