I have Universal Class Library (.dll) to share between projects. In the dll I have several resources .resw files dll\rootFolder\Lang\ en.resw , fr.resw , jp.resw.
In my app I have button "Change Language" clicking on which I want change app language like many web sites but the problem is that I can't get this files when clicking on the button using Resources.ResourceLoader()
I believe you haven't placed your resources in the right folders. You should create a structure like this:
strings\en\resources.resw,string\fr\resources.reswetc...Then you use the ResourceLoader to get access to your files and resources
You can check the official sample for application resources as it demonstrates everything that you seem to require in your code.