Tomaš Špidlík (1919–2010) was a Roman Catholic patristics scholar from the Czech Republic. The Spirituality of the Christian East is an excellent and concise encyclopedia on its stated topic. In the book, Špidlík systematically summarizes the spirituality of eastern Christianity and tells you where to look to learn more.
However, many of the doors that lead to more knowledge will require one of the following keys: English, French, German, Latin, Greek, Spanish, or Russian. Probably some Czech too.
For English-only readers, these bibliographies are still useful. But I appreciated the reminder of why it’s important for theologians to not be English-only readers.
Beyond the bibliographies, I also enjoyed the rest of the book! And I learned a lot. You might use The Spirituality of the Christian East as a supplement to the Encyclopedia of Ancient Christianity. While not nearly as comprehensive, it contains things EAC does not.