Here is the steps to enable regional language searching with Koha.

It works fine with my Koha and now I can search bibliographic details in Indian languages.

Open following file,  

Applications > Accessories > Terminal

sudo su

leafpad /etc/koha/zebradb/etc/default.idx

Find the line "charmap word-phrase-utf.chr" and comment it by inserting a # symbol.

The same line appeared in next paragraph too, do the same.

Add following line below the commented lines,

icuchain words-icu.xml

Rebuild zebra

sudo koha-rebuild-zebra -v -f library

Information courtesy: Bhaskar Ghosh, Gurudas College, Phoolbagan