I extended ResourceManager and replace the ResourceManager by the extended one, then added a pre build script to replace the ResourceManager to my own ResourceManager (Because of the auto-generation of designer).
The extended ResourceManager reads from a custom Resource file that contains all the captions in the system and reads the required Resource file based on the UI language.
In this way at runtime the extended ResourceManager will load all UI captions with the captions from the translated Resource file.
The Resource file contains all the resources in all resx files.