According to AACR2 23.2B1, a geographic heading is established in the official language of the country if there is no generally recognized English form.
The accompanying RI emphasizes the need for a recently published gazeteer in the language, and BGN decisions.

This means that almost every geographic heading must change to the vernacular form for each country, e.g. Belarusian towns in Belarusian, Georgian towns in Georgian, etc.
Previously, all geographic names of the Former Soviet republics were established in Russian (as the official language of the country).

• The changes in the language of geographic headings will occur in the following countries of the Former Soviet republics:

  Belarus Estonia Georgia (Republic) Kazakhstan Kyrgyzstan Latvia

  Lithuania Moldova Tajikistan Ukraine Uzbekistan

  In Eastern Europe, the changes will occur in the following countries:
  • Slovakia
  • Slovenia
  • Macedonia (Republic)

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  Examples

  According to RI23.4B, the qualifier of a qualifier drops out.

  NAFL926063
  151 0 Tver (Russia)
  451 0 ‡wnne‡aTver (R.S.F.S.R.)

  • The (Federation) drops out
  • Indirect subdivision goes through Russia (Federation).
    Art‡zRussia (Federation)‡zTver.

  But Prague (Czechoslovakia) changes to Prague (Czech Republic) since "Czech" is an adjective.

  151 0 Prague (Czech Republic)
  451 0 ‡wnne‡aPrague (Czechoslovakia)

  Indirect subdivision goes through Czech Republic, as normal.

  Art‡zCzech Republic‡zPrague.