I am currently learning to localize my L5 installation, thus, I am interested in this topic. As far as I can tell, the localization still works out of the box with L5. You have a default language set in the config and a fallback language. And according to my experience, this is fetching the respective language resource from the respective folders.

http://laravel.com/docs/5.0/localization

But L5 (and I guess L4 too) does not have a native multilanguage feature. You will probably have to install a package for that. Something like

https://github.com/mcamara/laravel-localization

Question: Where exactly did you try to use the 'trans' method? In a view file? I can only confirm that it works properly in view files so far...

Localization itself works out of the box in L4 and L5, but there is one difference: In L4 you could add whatever folder structure you like to your app/lang/{locale}/directory, you could easily access those files (even in subdirs) by Lang::get('directory_1.directory_2.[...].directory_n.key') in your views.

In L5 only those files in the directory resources/lang/{locale}/(without subdirs) are loaded. A value in resources/lang/en/foo/bar.php cannot be called in views by Lang::get('foo.bar.key') (which is by the way the same like trans('foo.bar.key')).

Having multiple lang files, I find it reasonable to organize those in several subfolders.

You may be right. I think I tried subfolders too at the beginning, but decided then to use underscores to "categorize" my language files, e.g. foo_bar.php. I will check asap. I will then also try other delimiters like '/'.

For your example you need to specify the path as:

trans('foo/bar.key');

For those who are facing the same problem with sub directories in Laravel 5. Its working, but you have to add a slash to the directories instead of a point.

e.g

{{ trans('foo/bar/foo.key') }}