Language negotiation configuration was under the (misleading) admin/config/regional/language/configure path in Drupal 7. However, it is not actually about configuring the languages (which happens on the page one level up at admin/config/regional/language and its subpages for each language). It is about configuring how the language is detected in the negotiation process, so the new path for this page is admin/config/regional/language/detection.
There are also changes to the callback names of the forms associated. The main form name changed from locale_languages_configure_form() to language_negotiation_configure_form(). It is going to be moved to language.module in a later patch, therefore the change in name prefix.