Your belief that "the maximum line height is the height of a capital letter and not the height of the accented character" is incorrect. Why? Because capital letters can take accents too, and accented capital letters are even taller than regular capital letters. Also, accented lowercase
letters can be taller than capital letters. Add to that the existence of letters with underhangs (e.g., the lowercase letters g and j), accents below
letters (e.g., the French letter Ç), and the possibility of multiple rows of accents (as in Vietnamese), and you can see that a font's line height definitely needs to be greater than the height of a regular capital letter (and most fonts, including BankGothic, take this stuff into account).
While it's technically possible to make accented letters no taller than regular capital letters, it's far from ideal. Sure, the default VF font of the localized versions manages to do this, but only by doing things like squashing the letter or shifting the letter down slightly (made possible by the two extra pixels of space below the letters), so it doesn't look all that great.
If you want to see what all the characters look like, check this out: https://dl.dropboxusercontent.com/u/89353583/FreeSpace/fs_font_chars.zip
. It contains a PNG of every character from every font of every version FS1 and FS2 that I could obtain, with duplicate font files omitted.
tl;dr: The issue at hand isn't something that can properly fixed by modifying the font. Requiring modders to reduce the height of accented characters just to fix the text positioning isn't a good idea because that would make such characters look unnecessarily worse than they should.