Development on https://drupal.org/project/config_translation reached a level that it was now ready to get into core. A record number of 27 contributors wrote patches, tested code, provided accessibility feedback, implemented responsive user interfaces, and so on (see http://winstondodger.com/posts/contributors-per-issue).
Sampling of user interfaces provided
Entry points provided are in-context (tab (2), operation for entity lists (4) and contextual link (3) as appropriate). For those without other admin permissions, there is a dedicated index of all translatable configuration (1):

The translate operations lead to a summary screen with language translation status and actions for editing/deleting and adding translations:

The overview screen delete operation leads to a standard confirm form (no screenshot here, its trivial). The edit/add operations lead to config schema based forms:

Module architecture
The new module is purely a user interface module (no settings provided even) that connects the already existing configuration API, the configuration schema API and the configuration language overrides. The high level structure of the module is as follows: .jpg)
Thanks to contributors!
vijaycs85, tstoeckler, webflo, Gábor Hojtsy, Schnitzel, falcon03, YesCT, kfritsche, Ryan Weal, dagmita, likin, toddtomlinson, nonsie, Kristen Pol, dawehner, tim.plunkett, penyaskito, EclipseGC, larowlan, robertdbailey, helenkim, David Hernández, EllaTheHarpy, lazysoundsystem, juanolalla, R.Hendel, Kartagis