The webpage uses jekyll. The template for the index is at _layouts/index.html.

If you want to add a new translation, follow these steps:

1. Copy index.html to index_{langcode}.html and update its lang value.
2. Copy _data/locales/en.yml to _data/locales/{langcode}.yml and update its initial language code.
3. Change the values of the English strings to the new, translated language strings.

You can see the translated webpage by running jekyll serve and opening http://localhost:4000/.