meetwp

Thanks for the feedback. It is good to know the method is still working fine.

Adding a subdomain solved the issue.
Here is a guide for other users
If you want to move from subdomain (en.topic1.com) to subfolder (topic1.com/en/) set the redirects with the following code in htaccess (code was provided by Ipstenu (Mika Epstein)).

Lesson #1: ALWAYS put the WP calls at the bottom.

Lesson #2: Always separate your .htaccess sections.

# Subdomains
RewriteCond %{HTTP_HOST} ^en.topic1.com [OR]
RewriteCond %{HTTP_HOST} ^www.en.topic1.com
RewriteRule ^(.*)$ http://topic1.com/en/$1 [R=301,L]

# BEGIN WordPress
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

# END WordPress

Wait a couple of hours as it did not work immediately.

If you are on the same server as the subdomains (en.topic1.com) was hosted you should have everything redirected.

If you are on a new server you must add a subdomain or the server will not know that for example en.topic1.com exists and will serve a 404
To do so, in cPanel, go to subdomains and create a subdomain pointing to the document root of the folder where the htaccess is. This will be the same folder which contains all the files for topic1.com

It should now work.

As a practical example, if anyone goes to http://en.meetitalia.org/travel-phrases/travel-phrases-1-ciao-hello/ he will be redirected to
http://meetitalia.org/en/travel-phrases/travel-phrases-1-ciao-hello/

remember that you must repeat the above steps for all subdomains you had on your previous installation.

And remember to thank Ipstenu (Mika Epstein) as it was her help that got me this far.

Hello, not completely solved.
If you are referring to this thread:
Thumbnail Captions (8 posts)
http://wordpress.org/support/topic/thumbnail-captions?replies=8
I have yet to figure out how to make the changes.

Thank you

Hello,
We decided to install everything from scratch on a new server.
We’ve exported and imported all content to the new site and are now ready to change dns
How can we set a redirect from en.topic1.com to topic1.com/en ?
I’ve googled for a few hours and found a few solutions, but none seem to work

Here is one of the solutions I found that was actually published by you

http://wordpress.org/support/topic/convert-subdirectories-to-subdomains?replies=18

# SubDomains
RewriteCond %{HTTP_HOST} ^subsite.domain.tld [OR]
RewriteCond %{HTTP_HOST} ^www.subsite.domain.tld
RewriteRule ^(.*)$ http://domain.tld/subsite/$1 [R=301,L]

Here are the current htaccess rules

# BEGIN WordPress
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{HTTP_HOST} ^en.topic1.com [OR]
RewriteCond %{HTTP_HOST} ^www.en.topic1.com
RewriteRule ^(.*)$ http://topic1.com/en/$1 [R=301,L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]
# END WordPress

Do I also have to create a subdomain on the new server Cpanel?
I’ve actually tried to do so, but had no luck in getting the redirect to work.

Thank you

Thank you for the helpful hint!