Mladen,
I also would like to better understand how it should work: I just had to rollback a site after having enabled content localization, because this messed up my host.

Enabling this feature did duplicate my tabs: the original tabs tree was kept for the portal default language (italian in this case), and a new tree of pages was created for en-UK (second language, en-US is disabled in this intranet site). But the problems were more: some of the modules in the "italian" tree lost their settings, while apparently most of the modules on the en-UK tree did not get any settings at all. Being in production I had no time to fix all of this, and had to restore my previous version.

If I understand, enabling this feature forces us to manage different tabs (and modules, and their settings) for each language: if you don't enable Content Localization, you can always live with localizable modules (say, magic content or Ealo HTML) and one only tree of pages.
Is this correct? Is there documentation about this new feature?

So what is the process of moving away from the Apollo MLHTML Module to the built in DNN 5.5 Localization Feature.