The most common and most likely answer to this crossword clue is the 10 letter word LINGUISTIC
I've seen this crossword clue in The Guardian
L
I
N
G
U
I
S
T
I
C
More clues leading to the result LINGUISTIC
Buddy explains!

The straight part
We know that "of tongues" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case of tongues = linguistic.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 LINGUISTIC mean?
LINGUISTIC adjective- Of or relating to language.
- Of or relating to linguistics.
- Relating to a computer language.