I noticed that Tildes docs make a point out of using words instead of labels. The stated reason is that icons may be difficult to understand, and I honestly don't get how is this the case.

Icons, when used right, are much more usable and intuitive than any text labels. They are small, distinct, they draw attention and you can tell what they do just by looking at them instead of reading them.

Take the classic upvote/downvote scrollers used on Reddit, Imgur, etc. It uses icons for upvotes and downvotes, but there isn't a single person I know who doesn't know what those mean. It's intuitive and usable. It doesn't require localization. It just works.

In contrast, the "Vote (10)" button on Tildes. It uses text, on a page full of text. It's an important UI element, one of the most used UI elements really, but it's not visually highlighted in any way. The amount of votes, which is an important metric, isn't distinct, making it hard to read. The "text button" style it uses is usually reserved for buttons that are used rarely, such as "Edit" or "Delete", or buttons that open more menus, such as "Edit" or "Reply". It's not intuitive.

Yes, this is a minor thing, but it's minor things that make the overall experience pleasant or unpleasant. And it shows how icons (and highlights), when used right, make user experience better.