Answer by Matthias Pfefferle for PHP Warning: Missing argument 2 for wpdb::prepare() WPML Plugin

$wpdb->prepare needs at least two params http://codex.wordpress.org/Class_Reference/wpdb#Protect_Queries_Against_SQL_Injection_Attacks

try something like that:

$wpdb->prepare("        SELECT p.ID, t.language_code         FROM {$wpdb->posts} p JOIN {$wpdb->prefix}icl_translations t ON p.ID = t.element_id AND t.element_type = CONCAT('post_', p.post_type)        WHERE p.ID IN(%s)", join(',', $missing_langs))