Add "show" method to language

This method allow user to get lang directly from view:

<?php echo \core\language::show('welcome_lorem', 'welcome') ?>

i know, i could change the method "load" and "get" to one, but then you
can not define the language of the file name in the constructor.

this additional method allow user to get language in view for eg.:

<?php echo \core\language::show('welcome_lorem', 'welcome') ?>

First param is a name of word in language file, second is a name of
language file, third optional is a lang code default third param get
value from LANGUAGE_CODE.