Zend_Search_Lucene works with UTF-8 charset internally. Index files store unicode data in Java's "modified UTF-8 encoding". Zend_Search_Lucene core completely supports it with one exception. ^[10]

Actual input data encoding may be specified through Zend_Search_Lucene API. Data will be automatically converted into UTF-8 encoding.

However, default text analyzer (which is also used within query parser) uses ctype_alpha() for tokenizing text and queries.

ctype_alpha() is not UTF-8 compatible, so analyzer converts text to 'ASCII//TRANSLIT' encoding before indexing. The same processing is performed during query parsing, so it's done transparently. ^[11]

Zend_Search_Lucene also contains limited functionaliy utf-8 analyzer. It can be turned on with the following code:

<?php
Zend_Search_Lucene_Analysis_Analyzer::setDefault(
    new Zend_Search_Lucene_Analysis_Analyzer_Common_Utf8());

It tokenizes data for indexing in UTF-8 mode and has no problems with any UTF-8 compatible character.

It has two limitations:

Because of these limitations it's not set as default, but may be helpful for someone.

Case insensitivity my be emulated with strtolower() conversion:

<?php
setlocale(LC_CTYPE, 'de_DE.iso-8859-1');

...

Zend_Search_Lucene_Analysis_Analyzer::setDefault(
    new Zend_Search_Lucene_Analysis_Analyzer_Common_Utf8());

...

$doc = new Zend_Search_Lucene_Document();

$doc->addField(Zend_Search_Lucene_Field::UnStored('contents', strtolower($contents)));

// Title field for search through (indexed, unstored)
$doc->addField(Zend_Search_Lucene_Field::UnStored('title', strtolower($title)));

// Title field for retrieving (unindexed, stored)
$doc->addField(Zend_Search_Lucene_Field::UnIndexed('_title', $title));

The same conversion has to be performed with query string:

<?php
setlocale(LC_CTYPE, 'de_DE.iso-8859-1');

...

Zend_Search_Lucene_Analysis_Analyzer::setDefault(
    new Zend_Search_Lucene_Analysis_Analyzer_Common_Utf8());

...

$hits = $index->find(strtolower($query));