Did you have a look at the section about localization at the end of the Plug-in developer's guide?

Yes I did. But that allows me to localize the strings I use on my plugin, not to get the existing localized strings on the application.

Of course if I want to put my plugin option on the "3D View" menu, for example, I can just get all the translations for "3D View" from SH3D source and put them on my plugin. But the problem is that if in the future the localized string for "3D View" on some language changes, then on that language there will be two "3D View" menus, one with my localization (which coincides with the former official localization before the supposed change) and one with the new official localization.

The same problem will occur if a new language is added which is not included on the plugin: duplicated menu.

If there is a way to get the localized string at runtime then the option will always be displayed on the correct menu. If currently there is not a way to retrieve these strings, I think it's a good addition for a future release to prevent these menu duplications by the plugins.