Have a long established v13 site. I need to add a language switcher and add additional languages. I've done this locally - setting certain doc types as having properties that can vary by culture. When I deploy changes via usync to test and import these changes all my content seems to become unpublished (though appears published in Umbraco, just complains about not being the cache). Anyone done this and know of any gotchas? I really need to be able to "upgrade" these sites to be multilingual without a rebuild.

When you switch from single to multilanguages the property values actually move a little internally in umbraco (previously they had no culture, and afterwards they will) the same happens with publishing. I would say make sure you do a full export of the site with uSync so you get all these changes as part of the sync

Hmmm it's a site with a lot of members and some custom tables full of wonder. Not sure that's an option here.

If your changing from a single to a variant side I would say both content and settings

Urgh - I've just realised I started this all a few months back when the site was in v10. I've just merged the dev branch back in - and starting trying to import a mess of v10 and v13 settings anyhow. I might need to go back to some basics here. OK - thanks for the pointers. I'll do some experimenting.

Another option (and I am thinking out loud) once you have all the settings synced/setup how you want them. Have done code to load every content node and then save and publish it, won't be fast but should force it all though the core umbraco code and make sure everything is updated as required??

I had thought that might be the only way.