Cannot select language for install on Wordpress

On the CiviCRM installer page on new Wordpress installation, having first uploaded other language files, even though I can select another language (in my case English UK) the language selector box flips back to English US.In additon, whenever language changed the content of the database fields then get reset - very frustraing loop that basically prevents me from installing CiviCRM in any other language.

Note: I noticed that installation URL has changed to reflect language selected i.e. en_GB so I went ahead with install, but regardless it still installed English US.