The most common and most likely answer to this crossword clue is the 12 letter word INARTICULATE
I
N
A
R
T
I
C
U
L
A
T
E
More clues leading to the result INARTICULATE
- Faltering Italian truce rewritten
- Tongue-tied single, taciturn with ale drunk
- Unintelligible irate lunatic going crazy
- Unable to speak, being delayed by hospital department after train crashed
- I rate lunatic terribly lacking in fluency?
- Trait in a clue that’s awful, not using words clearly
- Unable to speak, one copper gets delayed by fashionable painting
Buddy explains!

The straight part
We know that "lacking in fluency" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lacking in fluency = inarticulate.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 INARTICULATE mean?
INARTICULATE noun- An animal belonging to the subphylum Inarticulata.
- (of speech) not articulated in normal words
- Speechless
- Unable to speak with any clarity
- Not having joints or other articulations