The most multilingual Drupal release ever
Language handling improved
In Drupal 8, the new Language module serves the general language handling needs of the system (formerly part of Locale module). You can assign language to a lot more things, including taxonomy terms and even views or user role names. Language detection and selection is much improved with language mapping features, administration language preference and an independently configurable fallback language. Content language defaults and the user experience of assigning language is highly configurable. Finally, English can be removed from the list of configured languages.
Software interface translation automated
Now software interface translation has its own module (Interface translation). The full power of Localization update is built-in and its apparent from the first screen of the installer. You can interactively pick any language supported and the translation is downloaded live. Translation updates for modules, themes and distributions are also built-in. The system tracks and protects customised translations, so you can diverge from the community translations as needed. Translation downloads are now managed in one directory for easy deployment. The built-in translation user interface is highly improved. Finally, English strings can be changed as well, no need to add a custom English language.
Content translation is more flexible
The Drupal 7 content-copy based translation method is out and instead Drupal 8 has a field based content translation solution. This therefore applies to all kinds of content, including user profile fields, taxonomy term fields, commerce product fields, etc. Node built-in fields are also translatable and there is work ongoing to make other built-in fields (menus and taxonomy terms most importantly) translatable. Translation can be configured on a content type basis per field and for some fields even on a sub-field level (such as image fields with alt text and title). Search indexing per language and access control per language is supported.
Configuration translation added
There is now full built-in support for translating configuration, and all of it. You cannot just translate the site name or names of the built-in user roles and input formats but also views, menus, contact categories, and so on. Drupal tracks language for each configuration file, so it can translate shipped configuration from English to other languages, even as part of software translation downloads. Custom created configuration can then be translated from their own language as well. A simple but full user interface is included to support the process.
Drupal was never as multilingual as Drupal 8 is. Read more in an article series by Gábor Hojtsy.