Magento’s 1.8.1 Theme Translation
Learn how to translate specifically for your theme.
Magento has done a really good job in terms of not allowing you to mess with the core system. Everything in it is modular and hierarchical. So is it’s translation system. Read more on that here.
Translation files for its locale you are using are located in /app/locale/[locale]/.

But working with many themes AND more than two locales you will find your self a lot having different translations for each project. You may need to say “Shop now” in one project and “Buy it” on onother. Instead of changing the core .phtml files of your template and messing with the main locale folder, you can have different translations for each theme, so for each project. First add a “locale” folder inside your template folder.

Put your locales there in folders with a “translate.csv” within and make all your theme specific translations in there.

Make sure you have define it in you System->Configuration->Design properties, choose your main locale or a locale for each of your Store Views and of course clean up your cache.

And voila! Theme specific translations for Magento. Now you can carry on your main translation files (app/locale/) across different projects and change only your translate.csv file.
Thank your for reading. Hope i helped somebody.