The language support is quite impressive with support for latin, CJK and even indic scripts. Notable omissions include RTL scripts like Arabic and Hebrew.

From: https://support.google.com/faqs/faq/6188721

At the moment Google Handwriting Input supports 82 languages: Afrikaans, Albanian, Azerbaijani, Basque, Belarusian, Bengali, Bosnian, Bulgarian, Cantonese, Catalan, Cebuano, Chinese, Chinese (Simplified), Chinese (Traditional), Croatian, Czech, Danish, Dutch, English, Esperanto, Estonian, Filipino, Finnish, French, Galician, German, Greek, Gujarati, Haitian, Hindi, Hmong, Hungarian, Icelandic, Indonesian, Irish, Italian, Japanese, Javanese, Kannada, Khmer, Korean, Kurdish, Kyrgyz, Lao, Latin, Latvian, Lithuanian, Macedonian, Malagasy, Malay, Malayalam, Maltese, Maori, Marathi, Mongolian, Nepali, Norwegian, Nyanja, Odia, Polish, Portuguese, Punjabi, Romanian, Russian, Serbian, Sinhala, Slovak, Slovenian, Somalian, Spanish, Sundanese, Swahili, Swedish, Tamil, Telugu, Thai, Turkish, Ukrainian, Vietnamese, Welsh, Xhosa, Zulu