The problem seems easy to solve – I have installed multisite network, each new page have Polish language set as default, polish localisation files are in right directory, in wp_config there is line:
define(‘WPLANG’, ‘pl_PL’);
Sites admin panels are correctly in polish language, but global network admin isnt.
What am I missing to turn network admin panel to polish language?
Multisite Network Localisation
Re-saving the language of the first site with the ID #1 solved the problem.
One can do this within Settings » General » Site Language