Hi
When you enable the multilanguage, joomla recognizes that the first category is meant to be used for language so it is hided everywhere.
Not at all. Joomla doesn't care about the categories and do not know whether this is a language or anything else. It doesn't hide them, simply because it doesn't know this is a language category. The top category simply has no meaning on multillingual systems (nor in single language sites).
From a SEO standpoint, It is actually not recommended to separate content using a top-level language category anyway.
What's happening is more simple:
- Joomla uses menu items to build URLs
- sh404SEF uses articles titles and categories to build URLs: you have multiple settings under the "Extensions > Joomla" tab of sh404SEF configuration to decide how you URLs will look.
- having a language code inserted in the URL is decided upon in the Joomla system language filter plugin. The only option there is to hide or show the language code on the default language.
Please note that after changing sh404SEF settings that alter URL structure, you'll have to Purge URLs, so that new ones are recreated.
Rgds