Original:
http://forums.aeriagames.com/viewtopic.php?t=613555
But I can't follow the steps properly on W7..
Anyhow, here's a solution.
I used the font Calibri here. It makes stuff easier. And I can't find another way to do this..sorry. ><
1.) Open Windows' Fonts folder. [You could just type "fonts" on search when you open up the Start Menu and hit enter.]
2.) Open Grand Fantasia folder and open font.ini.
3.) With your Grand Fantasia folder still open, open up the "font" folder.
4.) Bring up the Windows Fonts folder and double-click on Calibri or any other Font. A Calibri sub-folder will pop up and copy one of those to Grand Fantasia's own font folder. You could keep or delete the other font there. You only have to directly copy the font if what you chose from Windows Fonts doesn't have font sub-types.

[In my case, I used Calbri Bold.]
5.) Switch to the .ini file and replace all (if you want everything to be written in the same font), with the font title. In Calibri's case, I just input Calibri. No space after each '=' sign.
6.) Copy the file name of the font you copied to GF's font folder.In here, replace the font name to that. [Again, in Calibri's case, 'calibrib' is the file name so I replaced the original font's name with that.]
Here's what it looks like now:
[FontOption]
// 字型設定
// 遊戲系統英文字型
DefEnglishFont=Calibri
DefEnglishFontSize=8
// 遊戲系統主要字型
DefMainFont=Calibri
DefMainFontSize=8
// 泡泡聊天字型
BubbleFont=Calibri
BubbleFontSize=8
// 區域抬頭顯示字型
HintFont=.\font\calibrib.ttf
HintFontSize=18
// 名條字型
HIDFont=Calibri
HIDFontSize=8
Here's another using Georgia:
[FontOption]
// 字型設定
// 遊戲系統英文字型
DefEnglishFont=Georgia
DefEnglishFontSize=8
// 遊戲系統主要字型
DefMainFont=Georgia
DefMainFontSize=8
// 泡泡聊天字型
BubbleFont=Georgia
BubbleFontSize=8
// 區域抬頭顯示字型
HintFont=.\font\Georgia.ttf
HintFontSize=18
// 名條字型
HIDFont=Georgia
HIDFontSize=8
Replace the info in the original font.ini file with this and just copy georgia regular into GF's font folder..
Mod Edit: Stickied