Issue #2687851 by quietone, mikeryan, heddn, xjm, catch: Refactor run() method on Migrate UI batch and remove the $operation parameter

Issue #2225293 by maxocub, penyaskito, Gábor Hojtsy, quietone, mitrpaka, Sonal.Sangale, rvilar, phenaproxima, Ryan Weal: Migrate D6 and D7 language negotiation settings

Issue #2353709 by quietone, maxocub, sidharthap, phenaproxima, Gábor Hojtsy: Variables to config: language.types [d7]

Issue #2821774 by tim.plunkett: MigrateUpgradeForm incorrectly using form values for multistep management

Issue #2809115 by petiar, Yogesh Pawar, maxocub: When migrating a multilingual D6 site, the overview page says that the translation upgrade path is missing

Issue #2657978 by maxocub, quietone, Gábor Hojtsy, Kristen Pol, alexpott:  Variable to config: language_default [d6]

Issue #2225775 by vasi, quietone, phenaproxima, chx, penyaskito, mikeryan, esclapes, vprocessor, steinmb, Gábor Hojtsy, Marc Angles, bwinett: Migrate Drupal 6 core node translation to Drupal 8

Issue #2682585 by heddn, dscl, hanoii, willwh, hussainweb: Rename MigrationCreationTrait as it no longer creates migrations - it configures them

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #2683421 by xjm, alexpott, hussainweb: Remove incremental and rollback options from the UI (and add them back when they are more stable)

Issue #2676222 by alexpott, johnrosswvsu: Move MigrationInterface out of the migrate\Entity namspace now they are plugins

Issue #2625696 by chx, benjy, alexpott, catch, mikeryan, andypost, phenaproxima: Make migrations themselves plugins instead of config entities

Issue #2281691 by xjm, mikeryan, Gábor Hojtsy, alexpott, tim.plunkett, webchick, abhishek-anand, quietone, yoroy, stevepurkiss, benjy, Bojhan, Ryan Weal, aleksip, anavarre, hussainweb, er.pushpinderrana, cilefen, Luukyb, Jo Fitzgerald: User interface for migration-based upgrades