Hi Paco,
maybe you are missing the most important thing about Tag Meta and how it works.

Both Tag Meta and ReDJ are URL based, this means each rule defines its URLs, because you can match one URL or many URLs thanks to regular expressions.

So the rule with ^/$ refers to a single URL, that is yourdomain/ and nothing more. The caret ^ means "start with" and the dollar $ means "end with". And this is the reason the rule works only on the homepage.

Probably you need just to create a main rule for each main language, so if you create a rule with ^/en this matches any URL like yourdomain/en/<any> and if you put this rule at the beginning (low ordering) and leave the flag "last rule" unchecked this rule will be applied for any URL, and if other rules will match they will be applied too (unless one of these rules has "last rule" set to true, then the process stops). So the "last rule" flag is really powerful, because it allows you to build "incremental" metadata for your pages...

Kind regards,
Luigi