[Koha] Koha search based on Language MARC fields

Hi, I'm Fairly new to KOHA Software and trying to understand the background scripting part of Koha for searching; My objective is: To customize basic search option to find all records/items based on language of the work/code-language, abstract language; for e.g fre could be marked in *any one* of three fields 008/35-37, 041 or 100l MARC fields. Presently, I made some changes to masthead.inc to have "language" option in drop-down of search index. it works only if language code is available in 041 field. It doesn't check for 100l and 008/35-37 MARC fields, which I need to enable. Please share any suggestions, directions, which perl or zebra confgi file to work upon. Thanks, Keeran