What language is the site using and what's that main language file's (e.g. lang.english.php for English) $locales set as?

The setting for the as-distributed English language file is
PHP Code:
global $locales;
$locales = ['en_US', 'en_US.utf8', 'en', 'English_United States.1252'];
@setlocale(LC_TIME, $locales); 
The site is using English and Dutch.
In lang.dutch.php the $locales are:
PHP Code:
global $locales;
$locales = ['nl-NL', 'nl-NL.utf8', 'nl-NL','nl'];
@setlocale(LC_TIME, $locales); 
No other problems with translations, only this one in the definition of
PHP Code:
'TABLE_HEADING_SPECIALS_INDEX' => 'Monthly Specials For %s', 
.

I temporarily changed the function zca_get_translated_month_name() to always use
PHP Code:
$month_name = strftime('%B'); 
Then the current Month is correctly translated in Dutch.
PHP Code:
$zcDate->output('%B'); 
seems to be not using the current $locales at this point?

Any idea/solution?

TIA,

jpda