extra_english.lang file not working

[Cranky Old Man]

Not all fonts support all possible Unicode characters (though i'm not sure if there is one that does). In order to determine if there is a lack of Unicode support based simply on what is rendered on the screen, you have to see if the font (or FNT) used supports the characters itself.

Done.

(I didn't bother with verifying C0, C1, Extended-A, and the basic russian alphabet, simply because there was so many characters to test.)

The following unicode blocks are confirmed to be at least partially directly supported in-game (using the default font "font_default.fnt"):
C0 Controls and Basic Latin - Basic alphabet (Control characters not supported by font.)
C1 Controls and Latin-1 Supplement - Letters with diacritics (for european languages) (Control characters not supported by font.)
Latin Extended-A - Latin characters
Latin Extended-B - Latin characters (Only these letters: ƒ, Ǻǻ, Ǽǽ, Ǿǿ)
Spacing Modifier Letters - Miscellaneous phonetic modifiers, and spacing clones of diacritics. (Only these: "ˆ", "ˇ", "ˉ", "˘", "˙", "˚", "˛", "˜" and "˝".)
Greek and Coptic - Greek alphabet (Probably every single character between ";" and "ώ". Characters "ʹ" and "͵" not supported by engine.)
Cyrillic - Basic Russian alphabet and Cyrillic extensions is at least supported by the font.
Historic Letters (only six) is supported by the font, but not by the engine.
Extended Cyrillic (Only the characters: "Ґ" and "ґ")