If you use rotated axis values by 1-89 degrees, then you might not see non-Latin letters. The reason is simple: when using rotated values, amCharts loads font_name.swf from fonts folder. In order to keep files smaller, only standard Latin letters, numbers and punctuation are included in these files.

Solution is quite easy if you have Adobe flash installed:

1) open tahoma.fla file from fonts folder
2) double-click on the square on the stage or on the "Symbol 1" in the library
3) click on the square on the stage so that it is selected. You should see text field properties in the bottom of the screen
4) in the text field properties, select the font you are going to use
5) click on the "embed" button
6) in the popup window, select characters you need to embed. The less characters you select, the smaller file size will be. You can try several different combinations if you are not sure which characters you need.
7) click OK, save your movie as your_font.fla and publish it.