In 2.6.12.1, except Benefits module, all other modules have been coded using Symfony framework. Therefore they use Symfony internationalization mechanism. You can get details on how to do the conversion manually from following article.
https://wiki.orangehrm.com/index.php/Ho ... mfony_CodeHowever in 2.6.12.1, not all the screens fully supported internationalization. Therefore there going to be a release candidate as 2.7-rc.1 which supports internationalization for all the screens except Benefits module. With 2.7 release candidate there will be a tool to do translations easily. Check OrangeHRM blog (
http://blog.orangehrm.com/) for more details. 2.7-rc.1 will go out by end of February.
Converting "lang_default_full" will help you to translate Benefits module. But for all other modules, translations should be done in Symfony way as mentioned in above article.