Stacks one phrase in Cyrillic or Latin script on top of another using Unicode characters from "Cyrillic Extended-A", "Cyrillic Extended-B", "Combining Diacritical Marks", "Combining Diacritical Marks Supplement".
Not all letters are in these blocks. For example, letters "j", "q", "ё", "э" and "я" raise a KeyError, "й" is substituted by "ü", and a lot of other Cyrillic letters are subtituted by their Latin look-alikes because of compatibility issues.
Despite the most recent characters used being added in 2008, a lot of fonts still do not support the characters, and some fonts support half.
Surprisingly, Iosevka, a programming font, supports all of the characters used, but Noto Sans, a font made to support all of Unicode, does not.