This page aims to document the Unicode coverage of all the fonts (including non-free ones) in Debian. It was created using fontforge, font-manager and gucharmap. You should also read the DebianInstaller/GUIFonts page to find out about the fonts used by the installer.
Please add any fonts which might fill in some of these blocks to the Fonts/Missing page.
TODO: automatically create this page based on the latest unicode-data package as well as all fonts in Debian unstable, using the fonts review:
https://pkg-fonts.alioth.debian.org/review/
Quick test
Firefox seems to render all Wikipedia languages:
http://meta.wikimedia.org/wiki/List_of_Wikipedias
https://phabricator.wikimedia.org/diffusion/MW/browse/master/languages/data/Names.php
Incomplete blocks
With missing characters mentioned, most of these are available as bitmap glyphs in Unifont or Unifont Upper.
Ahom: U+11740 to U+11746
Alchemical symbols: U+1F774 to U+1F776 and U+1F77B to U+1F77F
Arabic presentation forms-A: U+FBC2, U+FD40 to U+FD41, U+FD43 to U+FD46, U+FD48 to U+FD4F and U+FDFE to U+FDFF
Balinese: U+1B4C, U+1B7D and U+1B7E
Brahmi: U+11070 to U+11075
Chakma: U+11147
CJK strokes: U+31EF
CJK unified ideographs extension G: about 40 % of characters intermittently missing, from U+30041 to U+31328
CJK unified ideographs extension H: about 45 % of characters intermittently missing, from U+31353 to U+323A6
Combining diacritical marks supplement: U+1DFA
Cyrillic extended-D: U+1E04A and U+1E06C
Egyptian hieroglyph format controls: U+13439 to U+13455
Egyptian hieroglyphs: U+1342F
Geometric shapes extended: U+1F7D9
Glagolitic: U+2C2F and U+2C5F
Hebrew: U+05EF
Ideographic description characters: U+2FFC to 2FFF
Kaithi: U+110C2
Kannada: U+0CDD and U+0CF3
Khojki: U+1123F to U+11241
Lao: U+0ECE
Mongolian: U+180F
Musical symbols: U+1D1E9 and U+1D1EA
Oriya: U+0B55
Supplemental punctuation: U+2E57 to U+2E5C
Tagalog: U+170D, U+1715 and U+171F
Tangut components: U+18AF3 to U+18AFF
Telugu: U+0C3C and U+0C5D
Takri: U+116B9
Completely empty blocks
Most of these blocks have bitmap glyphs available in Unifont or Unifont Upper.
Chorasmian (U+10FB0...)
CJK unified ideographs extension I: (U+2EBF0...)
Cypro-Minoan (U+12F90...)
Devanagari extended-A (U+11B00...)
Dives Akuru (U+11900...)
Kaktovik numerals (U+1D2C0...)
Kana extended-B (U+1AFF0...)
Kawi (U+11F00...)
Khitan small script (U+18B00...)
Makasar (U+11EE0...)
Nag Mundari (U+1E4D0...)
Nandinagari (U+119A0...)
Old Uyghur (U+10F70...)
Ottoman Siyaq numbers (U+1ED00...)
Syriac supplement (U+0860...)
Tangsa (U+16A70...)
Tangut supplement (U+18D00...)
Toto (U+1E290...)
Unified Canadian Aboriginal Syllabics extended-A (U+11AB0...)
Vithkuqi (U+10570...)
Znamenny musical notation (U+1CF00...)
Some conscripts in the ConScript Unicode Registry (such as Klingon, Tengwar and Visible speech) have bitmap glyphs available in Unifont CSUR.