ISO 639-1
cu Church Slavic; Old Slavonic; Church Slavonic; Old Bulgarian; Old Church Slavonic
· filed 2026-07-18 · click a code to copy
Church Slavic; Old Slavonic; Church Slavonic; Old Bulgarian; Old Church Slavonic carries the ISO 639-1 two-letter code cu.
In practice this code appears in HTML (<html lang="cu">), HTTP Accept-Language headers, locale identifiers such as cu-XX, subtitle tracks and translation files — anywhere software needs to say “this content is in Church Slavic”.