Does Touch Bar Predictive Text Work for Languages Other Than English?
Yes, predictive text displayed on the Touch Bar does indeed work for other languages other than English, although it won't work for all languages.

In theory the language used by predictive text is a function of the preferred (i.e. primary) language set in the Language &amp; Region preference pane. While this defaults to a language based on the selected region, you can change it to another language manually (e.g. you live in the US but mainly work in French, so you still have the US set as your region but French set as your primary language). Note that by primary language I mean the one you have placed at the top of the Preferred languages list.

However, in practice (based on about 25 mins of testing using the Italian language), I had the following results:


YES, predictive text works with: system language, spellcheck and keyboard all set to Italian
YES, predictive text works with: spellcheck and keyboard set to Italian, while the system language is set to English
NO, predictive text does not work with: keyboard set to Italian, while both system language is set to English and spellcheck is set to Automatic.


NOTES:

1 Testing was conducted on 24 October 2017 using TextEdit on a 15" 2017 MBP with Touch Bar running macOS High Sierra 10.13 (Build 17A405).

2 By system language I mean the primary language set in the Preferred Languages list located at Apple > System Preferences > Language &amp; Region. If you have more than one language listed, then the primary language is the one listed at top.

3 By spellcheck I mean the 'Spelling' language set in Apple > System Preferences > Keyboard > Text.

4 By keyboard I mean the 'input source' set in Apple > System Preferences > Keyboard > Input Sources. Note that you can have multiple keyboards added here and it does not matter in what order they appear (i.e. I had Italian listed below English).