TYPO3 Core

I have a multilanguage site with 35 languages. Some of the langages use special letters like Russian, Chinese, Arabic, Thai and more. The site ist utf-8 encoded. Indexed search have the same configufarion for each language there is only the L parameter different. The search works for all languages except of Thai.
I have prove it in the database. The page for thai is indexed but the search find 0 records if i try to search some word.

Thai use such letters:
????????????????????????????????????????????????????????? (????????) ????
???????????????????????????????? ????????????????????????????????????????????????????????????????????????? ? ??????? ?????????????????????????????????????????????
??????????????????????????????????????????????????????
?????????????????????????????????????????????????????????????????????????????????
?????????????????????????? ????????????????????????????????? ??????????
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
????????????????????????????????????????????????????????????????????????????????????
??????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????????????????????????????????????????????????

Does known anyone why the search doesnt work. As i write above for china, russia and other languages with special character the search works fine, only the thai doesn't works.

(issue imported from #M9461)