Type lab
Five italic letters change with the language
Serbian and Russian Cyrillic use different italic forms for б, г, д, п and т. A browser can select the right glyphs when the font and language metadata agree.
The visible difference
In Serbian handwriting, italic д resembles a Latin g, п resembles an overlined u and т resembles an overlined Cyrillic ш. Russian typography commonly uses forms closer to ∂, n and m. Readers notice the mismatch even when they cannot name it.
How the browser chooses
OpenType fonts may carry both shapes under the locl feature. The browser activates the Serbian set when the content language is Serbian. A page marked sr-Latn can still select Serbian forms for a Cyrillic quotation because the language is Serbian even though the primary script is Latin.
Two causes of the wrong result
The font may not contain Serbian localised forms, or the page may have no correct language metadata. A neutral slanted font can also be acceptable because it does not imitate Russian handwriting.
Test the actual web file
Subsetting can remove OpenType substitutions. Test the same WOFF2 file that production serves, in an italic sample containing all five letters and the real page language.
The paired Serbian article includes browser measurements and live Serbian and Russian samples.