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
Ancient symbols: U+1019C
Arabic extended A: U+08D3 and U+08E2
Armenian: U+0560 and U+0588
Bengali: U+09FC to U+09FE
Bopomofo extended: U+31BC to U+31BF
Chakma: U+11147
Chess symbols: U+1FA00 to U+1FA53
CJK unified ideographs extension A: U+4DB6 to U+4DBF
CJK unified ideographs extension B: U+2A6D7 to U+2A6DD
CJK unified ideographs: U+9FF0 to U+9FFC
Combining diacritical marks extended: U+1ABF and U+1AC0
Devanagari extended: U+A8FE and U+A8FF
Enclosed alphanumeric supplement: U+1F10D to U+1F10F, U+1F16D to U+1F16F and U+1F1AD
Gujarati: U+0AFA to U+0AFF
Gurmukhi: U+0A76
Hebrew: U+05EF
Ideographic symbols and punctuation U+16FE1, U+16FF0 and U+16FF1
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, U+A7C2 to U+!A7CA, U+A7F5 and U+A7F6
Latin extended E: U+AB66 and U+AB6B
Miscellaneous symbols and arrows: U+2B97, U+2BC9, U+2BD3 to U+2BE7, U+2BF0 to U+2BFD and U+2BFF
Mongolian: U+1878
Newa: U+1145A, U+11460 and U+11461
N'Ko: U+07FD to U+07FF
Oriya: U+0B55
Sharada: U+111CE and U+111CF
Sinhala: U+0D81
Supplemental punctuation: U+2E4A to U+2E52
Syloti Nagri: U+A82C
Takri: U+116B8
Tangut U+187F2 to U+187F7
Tangut components U+18AF3 to U+18AFF
Telugu: U+0C77
Vedic extensions U+1CF7, U+1CFA
Completely empty blocks
Most of these blocks have bitmap glyphs available in Unifont or Unifont Upper.
Chorasmian (U+10FB0...)
CJK unified ideographs extension G (U+30000...)
Dives Akuru (U+11900...)
Elymaic (U+10FE0...)
Indic Siyaq numbers (U+1EC71...)
Khitan small script (U+18B00...)
Lisu supplement (U+11FB0)
Makasar (U+11EE0...)
Medefaidrin (U+16E40...)
Nandinagari (U+119A0...)
Nushu (U+1B170...)
Nyiakeng Puachue Hmong (U+1E100...)
Ottoman Siyaq numbers (U+1ED00...)
Sutton signwriting (U+1D800...)
Syriac supplement (U+0860...)
Tangut supplement (U+18D00...)
Yezidi (U+10E80...)
Some conscripts in the ConScript Unicode Registry (such as Klingon, Tengwar and Visible speech) have bitmap glyphs available in Unifont CSUR.