Language variables

In php I did a solution where I had a language file with different
language variables like:

if($_SESSION['lang'] == 'en') {

$start_body = 'Welcome';

}

if($_SESSION['lang'] == 'se') {

$start_body = 'Välkommen';

}

This file was included on every page. In the files I used the variable.
When the user selected the language that was set in the session, so
every variable content reflected the correct language.

Where is the best place to store these variables in RoR?

Suggest you use the gettext gem for L10n.

Isak