Switch from directory to file format in Astro - #2356

Changed pages include:

• 404.html - view
• de.html - view
• en.html - view
• es.html - view
• fr.html - view
• it.html - view
• ja.html - view
• ko.html - view
• pt-br.html - view
• zh-cn.html - view

There are more changes not included in the list