From the International section of
Apple's Catalina Features Page.
+Cantonese keyboard predictions: The new Cantonese predictions for Traditional Chinese Cangjie, Sucheng, Stroke, and Handwriting keyboards bring more relevant character and emoji predictions to Cantonese users.
+Improved Japanese predictions: A new neural language model takes words typed earlier in the sentence into account, so predictions are more grammatically consistent and relevant to the subject matter.
+New fonts for Indian languages: Get 34 new fonts, including four system fonts and 30 document fonts, for languages like Gujarati, Hindi, Kannada, Odia, Punjabi, and many more.
+New Indian English Siri voices: All-new Indian English male and female Siri voices allow Siri to be more natural and expressive.
+New dictionaries: New dictionaries include Thai-English and Vietnamese-English.
The interface language of individual apps can now be changed independently of the system language.
Also it appears that Siri can now do
translation.
Plus I found new keyboards for Lao, Assamese, Bodo, Cantonese, Dhivehi, Dogri, Kashmiri, Konkani, Maithili, Manipuri, Marathi, Mongolian, Odia, Sanskrit, Santali, and Sindhi (but still no Amharic).