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.