Find a Language string to do be able to translate it

Yes i searched the two strings you providfed
'Next' => 'Next',
'Previous' => 'Previous',

in the path you
components/com_comprofiler/plugin/user/plug_cbconditional/plugin.cbconditional.php

but i could not find them in the php file so i could translate them to german. what i understood was that i have to search inside this php filt efor a string like 'Previous' => 'Previous', and translate it to 'Previous' => 'Vorherige', if i want to change it to german. is that right ?

You need to add them to your language file. They won't exist until you do so. Most incubator project language strings won't be in your language plugin(s).