Thai text don't have space between words. Usually, a dictionary-based algorithm is used to break string into words. For Lucene to be usable for Thai, we need to use an Analyzer that know how to break Thai words is needed.

Lucene now included ThaiAnalyzer (org.apache.lucene.analysis.th.ThaiAnalyzer).

After I read Confluence document, I know that I can switch Lucene Analyzer to others Analyzer such as German, Russian to support indexing on these language on Administration > Site Configuration > Formatting and International Settings Section > Indexing Language field.

But I didn't see Thai as a choice