I do quite a bit of work on multi-lingual sites, and as a polyglot myself, I love the i18n features of SilverStripe. One thing that comes up quite frequently is that a client wants to edit the translations for static text (i.e. the _t() function calls) on the website. While the Translatable module affords content editors the ability to edit dynamic text in the CMS, static text remains buried in cryptic PHP, left editable only by a PHP developer or a very well-instructed content editor.
In an effort to help our these clients and make my life a lot easier, I created a little module last year to support creating, editing, and filtering PHP language files from within the CMS in an abstraction of the original PHP file.
This module is on my Github at git://github.com/unclecheese/LangEditor.git
Take a look! Post your feedback! Enjoy LangEditor!