Issue “You need Articulate Localization to open this project”

That is what's politely called "unexpected behavior." Here’s some standard advice that the staff usually offers:

Quit Storyline and relaunch it.

If that doesn’t help, try to repair Storyline

• https://www.articulatesupport.com/article/Articulate-Storyline-360-How-to-Fix-Unexpected-or-Erratic-Behavior 

If all that fails to help, submit a case directly to the Articulate staff. You can do that here: https://access.articulate.com/support/contact

Because you need to publish now, here's another option that might work: Create a new Storyline project, and try to import all the slides from the project you can't open.

Chiming in to note I'm experiencing this issue as well. Restarting and reinstalling Storyline 360 does not change the issue, and the Storyline import workaround does not work since the file is seen by the software as incompatible. I plan to submit a case to Articulate for guidance. 

Igitur77​ & GraceMSH​: How frustrating! I can't replicate the issue, so this is definitely a job for the support staff.

Here's one more thing to try: revert to a previous version of Storyline. You can do that through the Articulate 360 app:

If that doesn't work, that's one more piece of information that might help the support folks.

StevenBenassi​, LaurenDuvall​, and EricSantos​: I'm tagging you to ensure this issue gets attention. 

I'm having the same issue. Restarting and reinstalling didn't work for me either. I sent in a support ticket, hopefully it's an easy fix!