Internationalization is an important concern for Magento merchants and developers alike. Often the most daunting task is actually determining what strings in a given site or module need to be translated.
To help alleviate the burden of performing a translation gap analysis, I created a well-received module to catalog untranslated strings for a given set of locales as they are discovered and make them available to merchants or developers by an easy to use Magento report, complete with the ability to export to CSV. The untranslated string logging is very flexible and can be easily customized using standard Magento system configuration.
More in-depth information can be found on my Classy Llama blog post, Magento Translation, Step Zero: What Must Be Translated?
Where to get it
The module can found on github: https://github.com/ericthehacker/magento-untranslatedstrings.
Please refer to the README — I pride myself on comprehensive documentation. As always, I welcome feedback, issues, and pull requests. :)