It could be the same problem as http://wordpress.org/support/topic/homepage-shows-posts-in-both-languages?replies=22
Could you add this line
$args = array_merge($GLOBALS['wp_query']->query_vars, $args); // don't reset other query_vars!just above:
query_posts($args);And if it solves your issue, report the problem to the theme author together with this link to the codex: http://codex.wordpress.org/Function_Reference/query_posts#Preserving_Existing_Query_Parameters