The approximate number of IMB--International Medieval Bibliography--records for items written in Slavic and East European languages is as follows:
Polish: over 12,000
Czech or Slovak: over 9,000
Russian: well over 3000
Hungarian: over 3000
Bulgarian: approx. 1600
Estonian: over 500
IMB uses the British Standard transliteration system (which is included in a table here) for Cyrillic scripts, in which (for example) "языческое" becomes "yazȳcheskoe," "любовные" becomes "lyubovnȳe," "варяги" becomes "varyagi," etc. This is however for texts older than 1975. For anything since then, British libraries use the American Library of Congress system, which is available here.
The International Medieval Bibliography indexes articles from journals, edited volumes, conference proceedings, collected essays, Festschriften and exhibition catalogs published since 1967, in over 30 languages. The search interface's default setting also provides access to the Bibliographie de Civilisation Médiévale, which is a project currently under development that is aimed at indexing all monographs published on medieval Europe, the Middle East and North Africa since 1957. Both collections are brought together by Brepolis Medieval Bibliographies, based in Belgium. The database has concluded partnerships with universities, national libraries, and specialized institutes in many countries across Europe and parts of the rest of the world. Very usefully, the coverage tab allows patrons to see exactly what the database holdings are based on. The interface is available in English, French, German, Spanish and Italian. Searching can be refined easily, and full-text is available through a separate procedure for which instructions are provided via a YTube video through an imbeded link.
After entering a thematic search "architecture-secular" AND "Russia" (the language of the search terms was provided by the database itself, we get the following results: