Magento 1 was littered with translation functions. Helper objects, block objects, and the PHP global namespace all had a
__ function or method.
Magento 2 does away with this. Core team developers have removed the
__ method from the base block and helper classes, leaving only the global
__ function for translations.
If that didn’t make sense: In templates you used to say
echo $this->__('Hello World');
Now you say
echo __('Hello World');