Lucene is not limited to English and any other language. To properly index text, you need to use a parser that is suitable for the index language you are indexing. Lucene analyzers work well in English by default. Lucene Sandbox has a number of other Analyzers, including those for Chinese, Japanese, and Korean.
Here is a list of analyzers that you can integrate with your Lucene.NET: https://svn.apache.org/repos/asf/incubator/lucene.net/trunk/src/contrib/Analyzers/
As you can see above, many languages are already included in the analyzers, and if they are not included, go ahead and create it, because if it is not listed only, no one has tried it yet, but this does not mean that it is not supported .
Also read this SO discussion Indexing Multilingual Content with Lucene.net