Atticus by default uses the English language to pre-generate Chapter Numbers within your chapters. However, you can absolutely change those to be a different language with a few work arounds!
To start, Atticus offers the following Chapter Number Views:
1 / Chapter 1 / One / Chapter One
So, in order to change these to a foreign language you'll want to utilities the Chapter Title and Chapter Subtitle settings.
For your Chapter Title, choose a font that offers a Google Font of of your desired language. You can find Google offers over 1500 different font options.
Then type in your new Chapter Number in your desired language within the Chapter Title section of Atticus:
Chapter Subtitle will now be your new Chapter Title.
Ensure your theme settings have the following settings on/off:
Chapter Number - Off
Chapter Title - On (with desired language for font)
Chapter Subtitle - On (with desired language for font)
Then you should be all set! Each chapter will need the Chapter Number added and your Chapter Title included in the Subtitle section.