Language support

I get this error
Fatal error: Call to undefined function get_blog_details() in /websites/123reg/LinuxPackage22/es/ca/pe/escapeinsnowdonia.co.uk/public_html/blog/wp-content/plugins/signup-language/signup-language.php on line 125

When trying to install the signup language pack

I have installed the languages BUT these do not show in the plugin list (should they)
I have reinstalled both - same error
Suspect I am doing something stupid (or simple) but ........

Any help appreciated

Ta