Authors - Ingy Emara, Rawan Waleed, Sherry Emad Abstract - This study analyses speech errors in individuals with Down syndrome (DS) in both Arabic and English, with a particular focus on errors that reduce intelligibility for automatic speech recognition (ASR) systems. It compares the speech errors that most significantly affect intelligibility in each language and investigates the factors underlying differences in ASR accuracy across Arabic and English DS speech. The findings indicate that ASR systems perform less accurately with Arabic DS speech, highlighting the need for larger and more diverse Arabic DS speech datasets for system training. The study also identifies several physiologically related speech errors that negatively affect intelligibility in both languages, including devoicing of stop consonants, lateralization of /r/, reduced pressure in /s/, and deletion of consonants and consonant clusters. In addition, certain errors were found to be language specific, such as the mispronunciation of uvular and pharyngeal sounds in Arabic and the frequent omission of /r/ and vowel centralization in English. These findings have important implications for speech therapy by identifying priority areas for intervention, and for the ASR industry by emphasizing the need to expand labelled DS speech datasets across languages to improve recognition accuracy.