Oзон and Озон look the same, but the first one starts with a Latin O rather than a Cyrillic О. Searching for either will not find the other. These errors are not common, but they do occur on many wikis.
We can attempt to map homoglyphs (characters that look the same, like O and О) in mixed-script tokens and additionally index any single-script variants we can generate.
Original Title: Russian characters not normalized to same form in search
These look the same, or at least render the same, but only one of them returns results:
a: Oзон b: Озон