Resume on my two problems.
1)
Locale issue. The way Arena provides localization proved to be codepage-sensible. In my case, codepage for upper bytes is always cp1251, which contains Russian letters. Arena in some way wants to have letters with German Umlauts. When it does not find them in dialog item names, these items become untranslated.
However, Russian langfile from Yuri Voronov works fine, even with Umlauts. I don't know why
2)
Screen resolution issue. My settings of choice (which provide the best view on my LCD, and I don't want to change them) are 1600x1200, and 120 DPI fonts. I was told that is is typical glitch for Borland/Delphi-style GUIs, when some specific property is not set for controls. Having all other controls in Arena work well, I hope to see that fixed in the next releases. Really, I see no reasons for Arena to be DPI-sensible in 2009
BTW, Christopher, it looks like the problem is not BKAC, is it?
99.9% of programs on my box behave correctly independably from OS settings.
Anyway, my big thanks to all people who answered and helped to find out the reasons of these bugs. Thanks to the author of Arena 2.0 (really fine GUI) as well. Happy New Year!