I have some issues regarding resource assemblies in fody.costura. It could be that I'm doing something wrong.

When I add some localization resources they are not merged in correctly.
I added two projects to my fork of FodyAddinSamples to demonstrate the issue.
Both projects are working if the resources exists in their according folders. But if I delete the language folders (as seen in TestFixtureSetUp) then the localization is not working anymore.
For the internal resources the detailed log showed that Fody runs before satellite assemblies are created. And for the external resources (my most important use case) I have no idea what happens.

Maybe the bugs on MS side, as stated in this comment at Issue #52, are the reason for this.

IMHO the main point is that the satellite assemblies are not found or still not exist at compile-time when Fody is called.
Your internal test is working, since the resource file is added manually by code and not searched and added by Fody's msbuild target.

One point I want to mention is that everything is fine when I add the resource as reference. But then I can only add a single translation dll. I can add an example for this as well, if it makes sense.

I'm willing to provide a pull request as fix, but I have no glue where ti start right now.

So far and many thanks for Costura-Fody.
Dominik