LanguageTool supports several languages to a different degree. This page lists the number of rules per language to give a very rough indication of how well a language is supported.

Rules in LanguageTool 1.2
Date: 2011-01-02

XML rules    Java rules    False friends    Rule Maintainers
Belarusian7 (show/browse)0 0Alex Buloichik
Catalan213 (show/browse)1 4Ricard Roca
Danish22 (show/browse)0 0Esben Aaberg
Dutch302 (show/browse)0 0Ruud Baars
English478 (show/browse)3 230Marcin Miłkowski, Daniel Naber
Esperanto75 (show/browse)0 0Dominique Pellé
French1676 (show/browse)1 5Agnes Souque, Hugo Voisard (2006-2007)
Galician166 (show/browse)0 6Susana Sotelo Docío
German137 (show/browse)8 88Daniel Naber
Icelandic39 (show/browse)0 0Anton Karl Ingason
Italian86 (show/browse)0 36Paolo Bianchini
Lithuanian4 (show/browse)0 0Mantas Kriaučiūnas
Malayalam18 (show/browse)0 0Jithesh.V.S
Polish1027 (show/browse)4 139Marcin Miłkowski
Romanian418 (show/browse)1 0Ionuț Păduraru
Russian117 (show/browse)3 0Yakov Reztsov
Slovak55 (show/browse)2 0Zdenko Podobný
Slovenian58 (show/browse)0 0Martin Srebotnjak
Spanish64 (show/browse)1 27Juan Martorell
Swedish26 (show/browse)1 5Niklas Johansson
Ukrainian8 (show/browse)1 0Andriy Rysin

The number of Java rules listed is only the number of rules specific to that language. There are some rules that deal with punctuation and that apply to almost all languages.