multilingual redirect not working anymore after wordpress/apache upgrade

Greetings,

I had on a Centos 4 server two blogs running on wordpress 3.1.1 and apache 2.0. They were set up and worked perfectly to mimic one bilingual blog with the technique explained here:

https://freesoftware.zona-m.net/how-to-make-a-multilingual-wordpress-blog-without-multilingual-plugins/

this week I have moved those two blogs on a centos 6 server with apache 2.2, and they still work fine.

There was on the old server also another blog, running wordpress 3.0.1, and the multilingual plugin. I have migrated that other blog to the new one (centos 6 + apache2.2) and it works fine.

However, if I try to split it in two separate installs, again following the same technique explained here:

https://freesoftware.zona-m.net/how-to-make-a-multilingual-wordpress-blog-without-multilingual-plugins/

the redirects stop working. Every /it/ URL is not pointed to the right directory anymore.

I have installed the AskApache RewriteRules plugin on all blogs. The only difference I see is that

on the wordpress 3.1.1 blogs (the ones working) use_trailing_slashes is TRUE

on the wordpress 3.0.1 blog, where redirects don’t work, use_trailing_slashes is FALSE

Now:

can this be what makes the redirects fail?

(above all) since the server is the same and the apache directives for all the blogs are the same, why is that setting different between wp 3.1.1 and 3.0.1 ?? Why/how/where does WordPress change it?

what else could cause this problem?

Any feedback is really appreciated, thanks!