I'm satisified with the solution thus far, since I should at least be able to do everything that I want to do. I'm kind of surprised at the decision to use separate folding for different languages; I know that some letters are considered not equal to their diacritic-less equivalents, but I would have imagined that the problem here (if it is even a problem; I'm not sure that folding these wouldn't be desirable regardless; after all, we do already fold near-matches, don't we?) is worth the overhead of determining and implementing separate folding heuristics for each language.

I would imagine that universal folding would be helpful—especially given the sense that we print inexact matches anyway—but I am only an English speaker.

@Deskana It affects other scripts than Greek (e.g. searching for емкостях will not yield ёмкостях, etc.) and more sites than en.wikt (de.wikt and el.wikt, as well as en.wp and de.wp, and almost certainly others). It does not seem to affect el.wp—although I can't tell whether the problem has also been solved there in other scripts, or whether just a partial workaround has been implemented.

https://bugs.php.net/bug.php?id=69267 has been filed.