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 explicitly mentioned, most of these are available as bitmap glyphs in Unifont or Unifont Upper.
Arabic extended-A: U+08B8 and U+08D4 to U+08E2
Arabic mathematical alphabetic symbols: U+1EEF0 and U+1EEF1
Armenian: U+058D and U+058E
Bengali: U+09FC and U+09FD
CJK unified ideographs extension F: U+2CEBO to U+2E277, U+2E279 to U+2E6E9 and U+2E6EB to U+2EBE0
Combining diacritical marks supplement: U+1DF6 to U+1DF9
Elbasan: U+10500 and U+10502 to U+10527
Enclosed ideographic supplement: U+1F260 to U+1F265
Georgian: U+10C7, U+10CD and U+10FD to U+10FF
Georgian supplement: U+2D27 and U+2D2D
Gujarati: U+0AFA to U+0AFF
Kana supplement: U+1B002 to U+1B0FF
Kannada: U+0C80
Khojki: U+1123E
Limbu: U+191D to U+191E
Malayalam: U+0D00, U+0D3B and U+0D3C
Miscellaneous technical: U+23FF
Myanmar extended-A: U+AA7C to U+AA7F
Old Hungarian: U+10C81, U+10C89, U+10C8B, U+10C90 to U+10C92, U+10C94 to U+10C98, U+10C9D to U+10C9F, U+10CA1, U+10CA8, U+10CA9, U+10CAC, U+10CC0 to U+10CF2 and U+10CFA to U+10CFF
Old Permic: U+10351 to U+10354, U+1035A to U+1035E, U+10363 to U+10365, U+10368 to U+1036C, U+1036E and U+10370 to U+1037A
Sinhala: U+0DE6 to U+0DEF
Supplemental punctuation: U+2E43 and U+2E45 to U+2E49
Supplemental symbols and pictographs: U+1F900 to U+1F90B, U+1F919 to U+1F91F, U+1F926, U+1F928 to U+1F93E, U+1F940 to U+1F94C, U+1F950 to U+1F96B, U+1F985 to U+1F997 and U+1F9D0 to U+1F9E6
Transport and map symbols: U+1F6D2 to U+1F6D4 and U+1F6F4 to U+1F6F8
Vedic extensions U+1CF7 to U+1CF9
Completely empty blocks
Most of these blocks have bitmap glyphs available in Unifont or Unifont Upper.
Adlam (U+1E900...)
Ahom (U+11700...)
Bassa Vah (U+16AD0...)
Bhaiksuki (U+11C00...)
Caucasian Albanian (U+10530...)
Chakma (U+11100...)
Cherokee supplement (U+AB70...)
Duployan (U+1BC00...)
Glagolitic supplement (U+1E000...)
Grantha (U+11300...)
Hatran (U+108E0...)
Ideographic symbols and punctuation (U+16FE0...)
Kana extended A (U+1B100...)
Khojki (U+11200...)
Khudawadi (U+112B0...)
Mahajani (U+11150...)
Manichaean (U+10AC0...)
Marchen (U+11C70...)
Masaram Gondi (U+11D00...)
Mende Kikakui (U+1E800...)
Miao (U+16F00...)
Modi (U+11600...)
Mongolian supplement (U+11660...)
Mro (U+16A40...)
Multani (U+11280...)
Myanmar extended-B (U+A9E0...)
Nabataean (U+10880...)
Newa (U+11400...)
Nushu (U+1B170...)
Old North Arabian (U+10A80...)
Osage (U+104B0...)
Pahawh Hmong (U+16B00...)
Palmyrene (U+10860...)
Pau Cin Hau (U+11AC0...)
Psalter Pahlavi (U+10B80...)
Sharada (U+11180...)
Siddham (U+11580...)
Sinhala archaic numbers (U+111E0...)
Sora Sompeng (U+110D0...)
Soyombo (U+11A50...)
Sutton signwriting (U+1D800...)
Syriac supplement (U+0860...)
Takri (U+11680...)
Tangut (U+17000...)
Tangut components (U+18800...)
Tirhuta (U+11480...)
Warang Citi (U+118A0...)
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.