class="current" in menu

Look 3 screenshots for you

https://yadi.sk/d/yBPyqrs1MANFe
https://yadi.sk/d/ydwn3_JvMAMQi
https://yadi.sk/d/jABESz87MAMg4

need change in admin.php

$links[] = '<a href="' . admin_url( 'admin.php?page=akismet-key-config' ) . '">'.__( 'Settings' ).'</a>';

to

$links[] = '<a href="' . admin_url( 'plugins.php?page=akismet-key-config' ) . '">'.__( 'Settings' ).'</a>';

https://www.ads-software.com/plugins/akismet/