Hi!
Two taxonomies are associated to categories: "term_language" and "term_translations". The first is used to associate the language to the category. The second allows to group translations. pll_asf5vdg67 is just a unique id for such translation group. The value doesn't matter. It just has to be unique. Also it's important that the term description contains a serialized array of term_ids of linked translations. So each category should have 2 entries in wp_term_relationships, one for for the language, one for the translation group (even if the category is not translated).
More info on WP database: http://codex.wordpress.org/Database_Description
Reading the code of WPML to Polylang may help you too.