The font-language-override CSS property tells the font which language's glyph forms to use, overriding the lang attribute. This matters most for Cyrillic languages, Turkish, and others where italic or contextual glyph forms differ significantly between languages sharing the same script.
font-language-override CSS support…
The letters below render in italic using the current font. The left glyph uses the default (Russian/generic) Cyrillic form; the right uses the language-specific form requested by font-language-override. Differences are most visible in italic weight.