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
Arabic: U+061D
Arabic extended-A: U+08B5, U+08C8 to U+08D2 and U+08E2
Arabic presentation forms-A: U+FBC2, U+FD40 to U+FD4F, U+FDCF and U+FDFE to U+FDFF
Balinese: U+1B4C, U+1B7D and U+1B7E
Bopomofo extended: U+31BC to U+31BF
Brahmi: U+11070 to U+11075
Chakma: U+11147
CJK unified ideographs: U+9FF0 to U+9FFF
CJK unified ideographs extension A: U+4DB6 to U+4DBF
CJK unified ideographs extension B: U+2A6D7 to U+2A6DE and U+2A6DF
CJK unified ideographs extension C: U+2B735 to U+2B738
CJK unified ideographs extension G: U+30000 to U+30728, U+3072A to U+30EDC, U+30EDF to U+3106B and U+3106D to U+3134A
Combining diacritical marks extended: U+1AC1 to U+1ACE
Combining diacritical marks supplement: U+1DFA
Currency symbols: U+20C0
Enclosed alphanumeric supplement: U+1F10D to U+1F10F, U+1F16D to U+1F16F and U+1F1AD
Geometric shapes extended: U+1F7F0
Glagolitic: U+2C2F and U+2C5F
Hebrew: U+05EF
Ideographic symbols and punctuation U+16FF0 and U+16FF1
Kaithi: U+110C2
Kana extended-A: U+1B11F to U+1B122
Kannada: U+0CDD
Latin extended-D: U+A7C0, U+A7C1, U+A7D0, U+A7D1, U+A7D3, U+A7D5 to U+A7D9 and U+A7F2 to U+A7F4
Mongolian: U+180F
Musical symbols: U+1D1E9 and U+1D1EA
Oriya: U+0B55
Supplemental punctuation: U+2E53 to U+2E5D
Supplemental symbols and U+pictographs: U+1F979 and U+1F9CC
Symbols and U+pictographs extended-A: U+1FA7B, U+1FA7C, U+1FAA9 to U+1FAAC, U+1FAB7 to U+1FABA, U+1FAC3 to U+1FAC5, U+1FAD7 to U+1FAD9, U+1FAE0 to U+1FAE7 and U+1FAF0 to U+1FAF6
Tagalog: U+170D, U+1715 and U+171F
Tangut components U+18AF3 to U+18AFF
Telugu: U+0C3C and U+0C5D
Takri: U+116B9
Transport and U+map symbols: U+1F6DD to U+1F6DF
Vedic extensions U+1CFA
Completely empty blocks
Most of these blocks have bitmap glyphs available in Unifont or Unifont Upper.
Arabic extended B (U+0870...)
Chorasmian (U+10FB0...)
Cypro-Minoan (U+12F90...)
Dives Akuru (U+11900...)
Ethiopic extended-B (U+1E7E0...)
Indic Siyaq numbers (U+1EC71...)
Kana extended-B (U+1AFF0...)
Khitan small script (U+18B00...)
Latin extended-F (U+10780...)
Latin extended-G (U+1DF00...)
Lisu supplement (U+11FB0)
Makasar (U+11EE0...)
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.