I love that VisualEditor is aiming to make editing much more usable for newcomers, but many of the toolbar icons are unlabeled right now, or just have alt text for labels, which can be confusing for many people, especially people with less computer experience/confidence.
This is especially an issue when the icons use unfamiliar metaphors. The underlined italic A, the link icon, and the bulleted list icon may be reasonably familiar from other word processing interfaces, but the bookmark icon for citations and the omega icon for special characters were symbols I didn't immediately have confidence in understanding. The "hamburger" icon for more options is also likely to be unfamiliar for less experienced computer users.
Less experienced editors are likely to be hesitant to click icons experimentally if they don't know what they mean, since they're likely to be concerned that clicking the wrong button can mess something up or take an unexpected action that they won't know how to fix.
Here's an article about this type of design problem.
I'd suggest providing text labels in the toolbar along with icons for better usability for everyone! Having a complete set of alt-text captions (the kind that pop up after a moment of hovering, which several of the toolbar icons have right now) is important but I don't think that's enough for this interface.
The type of solution that Phabricator uses for labeling its editing toolbar icons (upon hovering you instantly get a popup of an obvious black-and-white text label) seems ok to me if varying lengths of labels in different languages is too much of a design problem.
