Create a validator which is looking for non-externalised strings on web-pages simular to eclipse non-ext string validator.
Here should be a prefference page for configuration validation and Quick fixes.
On configuration page user should be able
#1 disable or enable externalize validator;
#2 select warning level for validator messages(info, warning, error)
#3 select which attributes should be validated and for which tags(with some default pre configuration)

In Quick fix should be taken into account that same string can be already exist in props bundle.