Islandora aims to preserve as much of FedoraCommons underlying flexibility as possible, and to create a framework where users can create custom content models and ingest/display behaviours. Unlike earlier versions of Islandora, Islandora 7 Content Models are much smaller objects that are built (along with object behaviours/transformations) directly into code. This means that Islandora customization that involves creating a new content model and behaviours, or a new viewer, means writing Islandora code. Thankfully there are a number of resources available on the community page to help you get started. We also recommend reviewing the documentation available for developers on the Islandora Github wiki.
Islandora can be fully translated using the Drupal Internationalization (i18n) module. Please see the project documentation for more information. Tutorials are also available at http://drupal-translation.com/content/setup-multilingual-site.