And there are some features that could be into one or many contrib modules:

• Translations, which would provide the interface for content -node- translation. The existing hooks are more than enough to provide some translation interface and some links from one language version to another without needing more specific patches.
• Language icons, as a set of icons that can be used by any of these previous modules, or by the themes.
• Others, like 'translation workflows', 'collaborative translations', etc, etc...

Something that may need to be studied further, is how to keep the translation relations in the future. The separated tables in which translations are currently maintained, could be integrated in the main tables, just keeping the 'translation id' for each set of modules. Or maybe, if we have soon the new 'generalized relationships' feature some people is working on, translations could be kept using this feature as some special relationship between objects.