While the updated CMS area in Optimizely 12 has improved in many ways, some parts of the UI have been changed in a way that makes editing more difficult.
One such area is the language settings, where previously only languages that had settings associated with them were displayed. It was not until editing the settings that all languages were displayed. The UI is also more spacious now in general, with more padding and larger font sizes, which leads to less items visible at one time.
Furthermore, the popup is too narrow to display all columns when more than 4-5 languages are available for selection. Since the horizontal scrollbar now is placed under the language setting table, it makes it harder to navigate since you have to scroll down to see it.
These issues combine to make it harder to get a quick overview when editing language settings.
A final note is that the select boxes lack a focus indication, which makes tabbing through them when editing hard.
Please consider making a minor update of the UI with these points in mind in coming releases!