For issue 1: You could take a look at font such as Arial Unicode MS, which is considered almost "unicode complete", in that it implements the characters of most (all?) writing scripts in the unicode specificaiton.
Yeah, one might try some fonts that use thicker glyphs (e.g., Arial Black) for a workaround for this issue. But, that didn't work for Korean fonts that came with Leopard (and Tiger too). Those fonts display English characters with thicker glyphs, but won't do the same for Korean characters. I guess that is because Korean substitution for those fonts do not exist, thus the default font (such as AppleGothic) is used instead. I captured four screenshots showing this issue in detail. For all of them, I used the Text Renderer set to "Default" and the Default Encoding set to "Auto" in Leopard (10.5.7 Intel).
[Screen 1] font: Arial Black / subtitle encoding: CP949 / characters shown on the screen: English
http://img9.imageshack.us/img9/4656/ari ... 949eng.jpg
[Screen 2] font: Arial Black / subtitle encoding: CP949 / characters shown on the screen: Korean
http://img41.imageshack.us/img41/306/ar ... 949kor.jpg
[Screen 3] font: Arial Black / subtitle encoding: UTF-8 / characters shown on the screen: English
http://img198.imageshack.us/img198/6744 ... tf8eng.jpg
[Screen 4] font: Arial Black / subtitle encoding: UTF-8 / characters shown on the screen: Korean
http://img136.imageshack.us/img136/1183 ... tf8kor.jpg
I also checked Arial and Arial Unicode MS, but both of them were displayed with thin glyphs.
For issue 2: Another solution is just to convert your subtitle files to use UTF-8. I am not sure if the byte order mark is necessary.
I converted a subtitle file encoded in CP949 to be encoded in UTF-8, and it solved the problem. Thanks! However, I still think that the problem of resetting Default Encoding to "Auto" needs to be fixed. I'm not sure if this is a generic problem or something specific to my environment though. Is there anyone else experiencing the same problem as mine?