How Magento applies locales ?

When the locale is changed for a store, Magento searches and applies translations in the corresponding dictionaries in the following sequence:

  1. Module translations: <module_dir>/i18n/LOWEST PRIORITY
  2. Translation package: app/i18n/
  3. Theme translations:
    1. <parent_theme_dir>/i18n/ (iterated through all ancestor themes)
    2. <current_theme_dir>/i18n/
  4. Magento database – HIGHEST PRIORITY