I run a private wiki running Mediawiki 1.26.2. Visual Editor is stable and works well (I am using NetworkAuth to allow communication between Parsoid and MW), however enabling Lingo breaks Visual Editor returning HTTP 401 errors.
With the Lingo extension disabled it works perfectly well.
All that is changing is the line in LocalSettings.php
I installed within the mediawiki folder using:
php composer.phar require mediawiki/semantic-media-wiki "~2.0"
which returned no errors.
Happy to provide any useful debugging information, LocalSettings.php etc. etc.