The T2 bundle provides a variety of separate support functions, for
using Cyrillic characters in LaTeX: - the mathtext package, for using
Cyrillic letters 'transparently' in formulae - the citehack package, for
using Cyrillic (or indeed any non-ascii) characters in citation keys; -
support for Cyrillic in BibTeX; - support for Cyrillic in Makeindex; and
- various items of font support.