1) This is not easily possible. Maybe this could be done with a trigger event, etc. but I'm not sure because of various probles which can occur (long portfolio loading delay, etc.).
2) Yes - open up angular/includes/loop-portfolio.php and search for following line:
$output .= "<a href='#' data-filter='all_sort' class='all_sort_button active_sort'>".__('All','avia_framework')."</a>";
Replace the word All with any other text of your choice.
3) I think even WPML requires additional portfolio pages. You can try ajax translation plugins like: http://codecanyon.net/item/ajax-translator-revolution-wordpress-plugin-/1108823 or http://codecanyon.net/item/easy-translation-manager-for-wordpress/1187985 but I haven't tested them with Angular and I can't support them.