I suggest you a new and easy way for manage the localization.
Actually, every file in language directory contain all the key used in a specific module or page, but there are some function that use the same keyword or message.
For example, the keywords:
are used in many controller language file such:$_['entry_firstname'] = 'First Name:';
$_['error_firstname'] = '* First Name must be greater than 3 and less than 32 characters!';
My suggestion is to put all the common keyword in a single file, and use the specific files only for define the variation from the default value.
If there is no variation, is it not necessary to define the keyword.
What do you think about it?
Another good idea is to create a translator tool, that permit to display a table with the english (default) translator and an input text for insert the translation for the specific language.