Comment by raphlinus

I love this question. Basically all scripts have things that make them challenging to render, sometimes little things, sometimes bigger ones.

Cyrillic for Russian is reasonably straightforward, but it's also used for many other languages. The variation in style is particularly notable for Bulgarian[1]. A sophisticated font might have a "loca" table with locale-specific adjustments, but this is not universal yet, for example the issue to add it to Open Sans is still open[2]. To see the differences, try [3] and use the Language dropdown to select Bulgarian.

[1]: https://en.wikipedia.org/wiki/Bulgarian_alphabet

[2]: https://github.com/googlefonts/opensans/issues/114

[3]: https://localfonts.eu/freefonts/traditional-cyrillic-free-fo...