Question

I want to retrive post id inside plugin.
I tried

global $post;
 $a_Id=$post->ID; 

and

global $wp_query;
$thePostID = $wp_query->post->ID;

and

var_dump(get_the_ID()); //shows just null

How i can retrieve it?

The idea is to get language of post from Custom Fields
and feed it into Global Translator plugin as a BASE LANG

EDIT:
I can retrive id from $_GET[‘p’] on development server but on production i
have pretty urls so i dont have it.

Answer 1

Assuming that you know what the ID is for an particular post you could use

var_dump(get_defined_vars());

to show a listing of anything that you can get your hands on.
Look through the output for the ID that you know and then use the path that it shows to get there.