Currently these translations are available:

translation-en.json

translation-de.json

translation-es.json

translation-fr.json

translation-gl.json

translation-pt-BR.json

translation-ru.json

However you can create your own translation file for a new language.

1. Download the translations files of DocumentUltimate

2. Create this folder under your project: 

App_GlobalResources\WebViewer\i18n 

(note that before Version 4.3.0 - October 4, 2018 the folder was App_GlobalResources\WebViewer\Html5\Resources\i18n)

3. Copy translation-en.json file from this zip to this folder, rename the file according to the new language.

Make sure you are using the .NET standard codes for cultures:  

http://timtrott.co.uk/culture-codes/

For example translation-mr-IN.json for Marathi or translation-hi-IN.json for Hindi

4. Edit the text for this file to translate to your language and save the changes

Normally when you modify a file under App_GlobalResources, it should be recognized automatically. 

If not you can force AppDomain restart via touching web.config manually.