Fluency disorder means the intrusion or repetition of sounds, syllables, and words; prolongation of sounds; avoidance of words; silent blocks; or inappropriate inhalation, exhalation, or phonation patterns. These patterns may also be accompanied by facial and body movements associated with the effort to speak.
What is interesting is that a child who stutters in L2 (second language) may or may not stutter in L1 (native language). I have had two English learners who stuttered in English, one of whom stuttered in his native language, and the other who did not.