What about just counting or listing the classes and then work class by class? While an attribute may be an interesting idea, I'd regard it as over-engineered. Globalizing does nothing more than, well, going through each class and globalizing the code :)
You want to finish that anyway before the next release. So go ahead and just do it one by one, and there you have your progress. I'd regard a defect raised for each class as too much either.
In my last project, I started full globalization a little late. I just went through the list of code files, from top to bottom. Alphabetically in my case, and folder after folder. So I always only had to remember which file I last worked on. That worked pretty well for me.
Edit: Another thing: In my last project, globalizing mainly involved moving hard-coded strings to resource files, and re-generating all text when the language changes at runtime. But you'll also have to think about things like number formats and the like. Microsoft's FxCop helped me with that, since it marks all number conversions etc. without specifying a culture as violations. FxCop keeps track of this, so when you resolved such a violation and re-ran FxCop, it would report the violation as missing (i.e. solved). That's especially useful for these harder-to-see things.