Hi,
I'm getting the following when testing my apps in languages other than English:
Failed to load resource: the server responded with a status of 404 (NOT FOUND) https://*****-1edc3a4f15d104.sharepoint.com/sites/testfi/_catalogs/theme/Themed/634341C6/corev15app-DDE41C8D.themedcss?ctag=0
That error is from the browser web debug console and the App itself is completely broken as it has not loaded that stylesheet so no SharePoint styles / modals etc work.
This is a new issue as when I first published this particular App in late August it definitely WAS working in my test Project Online environment.
I'm planning on deploying an update to the store with the above file dynamically loaded from the host-web but this looks very much like a bug to me!
Martin Laukkanen (Project Server Blog - www.nearbaseline.com/blog)