After reviewing language support and translation for many of Drupal's pieces, we arrived at a pretty complex question, building multilingual navigation. The question is especially of importance because we often need to put translated content in menus, and the cross of translation of content and translation of menus can easily get us into the woods. Let's build some simple solutions for different use cases to see how to think of multilingual menus.
I know many of you faced the goal explained above. There are tools of different levels of involvement and there is of course no ready-baked answer to this question, but here is my best take so far for the current two active versions and Drupal 8 in development.
The three areas of Drupal language support
(A) First off, you can run a single language foreign language website without a need for content or configuration translation. Because the Drupal user interface comes in a flavor of English, you'll need to translate that. But all your content and configuration can be entered in your language, so you are fine there.
(B) Second, if you need to mark your content with language information, such as if you are running a multilingual blog, where you post in different languages, but will not translate your posts, you need language assignment with multiple language options.
(C) Finally, if you need to have the same content translated, the same navigation replicated or similar navigation produced for different languages, you need translation for your content and configuration.
The three types of data for Drupal translation
When it comes to translation, Drupal data can be separated to three buckets: (1) User interface (2) Content (3) Configuration. Drupal has very extensive support for user interface translation, I'd say too much support for content translation and usually not so bright support for configuration translation. Let's enumerate what Drupal has on offer for each piece.
As some of you might be aware, a group of talented and very determined people sprinted in Berlin about a month ago just to improve the i18n module for almost a week. A lot of great improvements made it in including tests, translatable contact forms and even some great usability improvements. Jose Reyero and Friederike Schmiedebach have great posts about the sprint.
My last post where I've explained how Internationalization module re-implements some of Field API and where it does not do that it misses crucial functionality did not get much discussion. Therefore I decided to turn the key point at the end to the center of discussion: that either Drupal core will do fields for all user input (content and configuration alike, all through form your site name to your views empty text), or i18n module needs to do it in contrib. There is a clear need for input widgets, validators, permission handling, storage and output formatters and rendering used consistently. If it is not done by core, it will keep being a bolted-on half-failing approach despite best efforts in contrib. Please discuss at http://groups.drupal.org/node/154434
The other important post that we need your input on is about removing all UI strings from code. There are various issues with having them in code, while there are also various disadvantages to removing them from there. There are performance, translatability and even user experience concerns involved. This post is already getting some discussion, but we need much more. This could be a huge, fundamental change, so all your input is welcome. Don't say we did not ask you. Please discuss at http://groups.drupal.org/node/154394
Your input helps shape Drupal 8 and how Drupal supports building multilingual sites for years to come. Have your voice heard now!
Regular readers could find this boring, but let's reiterate the three working modes that all objects should ideally be able to handle in Drupal to support multilingual site building.
Being able to mark an object as in one language.
Being able to mark an object as in one language and relate it to others as being a translation set. This is useful when you want to use the different language objects in different relations, track their history separately, have different permissions and workflows for them, etc.
Being able to translate pieces of the object that need translation and leave the rest alone. Load the right language variant of the object dynamically as needed. This is very useful for keeping external relations intact and sharing common fields between translations effortlessly.
There are certain things, where not all of these make sense. For the site's name for example, people would probably only use either (1) or (3). For a block for example, people should be able to use either based on their needs. (2) is useful to place blocks differently on translated pages, (3) is good to keep the placement consistent without effort. This can be different on a per-block basis. Same applies to nodes, menus, taxonomy, views, rules, and so on.