The PHP gettext extension requires a specific structure which will contain your translation files.
/path/to/your/translation_root/en_US/LC_MESSAGES/
/path/to/your/translation_root/en_GB/LC_MESSAGES/
/path/to/your/translation_root/fr_FR/LC_MESSAGES/
/path/to/your/translation_root/es_ES/LC_MESSAGES/
… and so on …
The language code is composed of two characters defining the language itself (en, fr, es, …) and two characters defining the country (US, GB, FR, ES, …).
The directory pattern is:
<path_to_where_you_want>/<ll_CC>/LC_MESSAGES/