I had the same issue with the fonts fontello and glyphicons. They were all gone when installing plone.app.multilingual. I first tried to recompile the bundles in Development mode, but that did not change the situation. I could not update the Registry "merge_with" to None solution as Daniel discribed above and I have no idea how and where to put his solution with the registry.xml file and the GenericSetup profile...
So I solved it in a complete different way (and I admit not expected...) by using the portal_quick installer and did the following. I discovered that sometimes a simple reinstallation solves some corrupt things (my 5 cents):
Go to ZMI /...yoursite.../portal_quickinstaller/manage_installProductsForm
- Reinstall Static resource storage
- Reinstall plone.staticresources EXPERIMENTAL: Async Resource Loading
Maybe the reinstall of Static resource storage is not needed, but I simply started with that step and then the second plone.staticresources EXPERIMENTAL: Async Resource Loading.
After refreshing my browser (to prevent Caching issues) I got all Icons back