I was using your Font Test mod with the English version--nothing from the international versions was used. In fact, I didn't realize that the language was still set to German. (I'm currently testing the SVN version of FSPort in German.) Setting it back to English or playing without your mod "fixed" the problem.
If you want the data from the German and Polish versions of the game (a true French version apparently doesn't exist), I have links to it at the end of this post:http://www.hard-light.net/forums/index.php?topic=85492.msg1709621#msg1709621
And if you want to see exactly what is in each font file, I've got dumps of them here:https://dl.dropboxusercontent.com/u/89353583/FreeSpace/fs_font_chars.zip
I haven't looked through your code yet, so I don't know what might be causing the problem.
I should say this, though: For all languages other than Polish, FreeSpace expects mission, campaign, and table files to be encoded in Windows-1252
; while loading those files, the game converts them to CP437
to match the fonts. (Technically, fiction viewer files should be in that list, but last I checked, no remapping took place there.) If the language is set to Polish, however, the files are supposed to be encoded in Windows-1250
, and no code-page conversion occurs. In all cases, though, the letter ß is converted to ss.
(And yes, Ż looks like Ƶ in the Polish font; from what I can tell, this is just a glyph variant in that language.)
If you have any further questions about FreeSpace localization or character sets in general, just ask me; I know quite a bit about those things, so I should be able to answer your questions.