As I said earlier, the language code is taken from Joomla language setting. So if your default language is Spanish, es-ES code will be passed to the system. and will be filtered by that code. Also if you are using joomla language switcher module, corresponding switched language code is used for displaying lists.
Please note that you need to set the language from category form page instead of manually setting in DB. 6 characters are used for future purpose.
CA is not yet ready and is in progress. Only CP can allow languages.
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