I installed the English Complete version and then applied HD textures; it now displays mana correctly! However, there's a problem: it doesn't display Russian text properly. Is there any way to install a Russian codec so that instead of gibberish, I see actual letters?
Consequently, this mana issue should occur for all Russian Complete versions when HD textures are installed on them.

There are different versions of Complete, and it's also possible that you're installing one version over another or patching incorrectly. The inability to see mana has been an ongoing issue since version 3.0, affecting localized versions starting from 3.2. This is controlled by the GENRLTXT.TXT file, which was originally published here.
The English version does not include Cyrillic characters in its fonts, and Windows isn't configured with the correct font substitution. That's why garbled characters appear. The simplest solution is to place Cyrillic fonts in the Data folder.