Double underscore in PHP
PhpSyntaxPhp Problem Overview
What does the double underscores in these lines of PHP code mean?
$WPLD_Trans['Yes'] = __('Yes', $WPLD_Domain);
$WPLD_Trans['No'] = __('No', $WPLD_Domain);
Php Solutions
Solution 1 - Php
It looks like you're using WordPress - wp-includes/l10n.php defines __ as a function that translates a string (similar to gettext and its alias, _, but with an optional parameter for explicitly specifying a domain).
Solution 2 - Php
Strictly speaking, it means nothing in PHP as it is not a pre-defined function. However, in many frameworks, like CakePHP, and other libraries the double underscore is a function used for translating strings based on the user's language/locale preference.
Solution 3 - Php
WordPress documents its __() function, and part of the localisation technology on Working with WordPress Core – Translate WordPress.
It is difficult to find documentation because __(), __('') or __("") is not very searchable. Double underscore and parentheses (round brackets) are some keywords to use.
Solution 4 - Php
As mentioned it is generally used for translating text between languages but really it is used in the same context as any function call.
testfunction();
is no different then
__();
Solution 5 - Php
A similar or third-party GNU gettext based implementation is gettext():
> Note: You may use the underscore character '_' as an alias to this function.