I'm trying to build a MySQL query to select last post by language (Polylang plugin) but I can't find what table and field does Polylang store the language of each post. Any clue?
I know it's too late to answer your question, but I gonna write it, for future users.
you can find everything related to Polylang in wp_term_relationships and wp_term_taxonomy tables.
for example, if I want to get the language of a specific post with id = 157896.
In the wp_term_relationships in object_id column I should search for 157896 and I will get
object_id | term_taxonomy_id
----------------------------
157896 | 26284
157896 | 26130
157896 | 11
and in wp_term_taxonomy we have:
term_taxonomy_id | taxonomy | description
---------------------------------------------
26284 | post_translations | a:2:{s:2:"en";i:157896;s:2:"de";i:157894;}
26130 | category | Description ... ...
11 | language | a:3:{s:6:"locale";s:5:"en_UK";s:3:"rtl";i:0;s:9:"flag_code";s:2:"en";}
26130 is related to the category
26280 means this post translated in de and en languages and the post number for en is 157896 and the post number for de is 157894
11 means the post with id = 157896 is in en(English) language.
wp_term_relationships is a pivot table.