How can i have a custom theme created by myself for multilingual site?
Theming pages based on node id is not the way to handle this because you will have to copy each template to the corresponding translated nids. 
A better approach is to create content types based on differences (which can be different layouts as well). 
You can create a content type "404_page" for 404 pages in each language and create a template node--404_page.tpl.php to style them. This is all node specific.


There are also page specific overrides like: 

page--front.tpl.php  
page--user.tpl.php  
page--blog.tpl.php    

Edit: Some extra information on Theme hook suggestions can be found on the Drupal 7 Theme Hook Suggestions documentation page.