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.
Adlam: U+1E94B
Ahom: U+1171A
Arabic extended A: U+08D3
Armenian: U+0560 and U+0588
Bengali: U+09FC to U+09FE
Chess symbols: U+1FA00 to U+1FA53
Devanagari extended: U+A8FE and U+A8FF
Geometric shapes extended: U+1F7E0 to U+1F7EB
Georgian extended: U+1C90 to U+1CBA and U+1CBD to U+1CBF
Gujarati: U+0AFA to U+0AFF
Gurmukhi: U+0A76
Hebrew: U+05EF
Ideographic symbols and punctuation U+16FE1 to U+16FE3
Kaithi: U+110CD
Kannada: U+0C84
Kharoshthi: U+10A34, U+10A35 and U+10A48
Lao: U+0E86, U+0E89, U+0E8C, U+0E8E to U+0E93, U+0E98, U+0EA0, U+0EA8, U+0EA9, U+0EAC and U+0EBA
Latin extended D: U+A7AF, U+A7B8, U+A7B9 to U+A7BF and U+A7C2 to U+A7C6
Latin extended E: U+AB66 and U+AB67
Miao: U+16F45 to U+16F4A and U+16F7F to U+16F87
Miscellaneous symbols and arrows: U+2BC9, U+2BD3 to U+2BE7 and U+2BF0 to U+2BFF
Mongolian: U+1878
Newa: U+1145E and U+1145F
N'Ko: U+07FD to U+07FF
Supplemental punctuation: U+2E4A to U+2E4F
Supplemental symbols and pictographs: U+1F90D to U+1F90F, U+1F93F, U+1F971, U+1F97B, U+1F9A5 to U+1F9AA, U+1F9AE, U+1F9AF, U+1F9BA to U+1F9BF, U+1F9C3 to U+1F9CA and U+1F9CE to U+1F9CF
Takri: U+116B8
Tangut U+17002 to U+17004, U+17006 to U+1702F, U+17032 to U+17037 and U+17039 to U+187F7
Tangut components U+1880C to U+1880F, U+18811, U+18813, U+18816 to U+18818, U+1881C to U+1881F, U+18825, U+18826, U+18829, U+1882E to U+18830, U+18834 to U+1883C, U+1883E to U+1884C, U+1884E to U+18852, U+18857, U+18859, U+1885A, U+1885D, U+1885E, U+18860, U+18865, U+18867, U+18868, U+1886B to U+1886E, U+18870 to U+1887C, U+1887E to U+18881, U+18883 to U+1889B, U+1889D to U+188AF, U+188B1 to U+188C6, U+188C8 to U+188D6, U+188D9 to U+188E8, U+188EA to U+18919, U+1891E, U+18921 to U+18942, U+18946 to U+18959, U+1895B to U+18975, U+18977 to U+18AD4 and U+18AD6 to U+18AF2
Telugu: U+0C04 and U+0C77
Transport and map symbols: U+1F6D5 and U+1F6FA
Vedic extensions U+1CF7, U+1CFA
Completely empty blocks
Most of these blocks have bitmap glyphs available in Unifont or Unifont Upper.
Dogra (U+11800...)
Egyptian hieroglyph format controls (U+13430...)
Elymaic (U+10FE0...)
Gunjala Gondi (U+11D60...)
Hanifi Rohingya (U+10D00...)
Indic Siyaq numbers (U+1EC71...)
Makasar (U+11EE0...)
Masaram Gondi (U+11D00...)
Medefaidrin (U+16E40...)
Mongolian supplement (U+11660...)
Nandinagari (U+119A0...)
Nushu (U+1B170...)
Nyiakeng Puachue Hmong (U+1E100...)
Old Sogdian (U+10F00...)
Ottoman Siyaq numbers (U+1ED00...)
Siddham (U+11580...)
Small Kana extension (U+1B130...)
Sogdian (U+10F30...)
Soyombo (U+11A50...)
Sutton signwriting (U+1D800...)
Symbols and pictographs extended-A (U+1FA70...)
Syriac supplement (U+0860...)
Tamil supplement (U+11FC0...)
Wancho (U+1E2C0...)
Zanabazar square (U+11A00...)
Some conscripts in the ConScript Unicode Registry (such as Klingon, Tengwar and Visible speech) have bitmap glyphs available in Unifont CSUR.