Note: an equivalent feature, [[https://bugs.launchpad.net/evergreen/+bug/1733695|Multilingual Search]], was introduced in Evergreen 3.1.

======Basic overview of the feature or change======
Proposed feature is to add capability for additional search target languages to be specified.\\
Currently, Evergreen only allows the language specified in MARC 008 position 35-37 to be the target of a language search.\\
There is no current mechanism to allow for additional languages to be included as search targets.\\
The proposed change would add a new table (metabib.language_filter e.g.). This new table would contain a tsvector datatype.\\
This tsvector would contain the languages associated with each bib record (tag 008 35-37 and selected 041 records).\\
Search code would be changed to join the metabib.language_filter table during the search query build.
=====An explanation of the existing code – it's structure and purpose – if applicable=====
=====An explanation of why this code needs to change, if applicable=====
These changes will allow an additional MARC tag (041) and subfields to be searched for language, beyond the standard tag 008 position 35-37.		
=====A full explanation of the new or replacement feature including implementation plans=====
This feature will allow staff to search for alternate languages, in addition to the primary language found in MARC 008 field position 35-37.\\
An additional table, metabib.language_filter, would be added. This table would include a tsvector, which contains a vector of languages associated with\\
a bib record. These languages could be searched by staff using the language pulldown, or the "item_lang" search line command. If no languages were\\
selected in the language pulldown, there would be no change to current search; the "default" language would be used in searching.
=====Analysis of what this change will effect in the existing code base=====
The following perl module would be modified:        
  * ./Open-ILS/src/perlmods/lib/OpenILS/Application/Storage/Driver/Pg/QueryParser.pm\\
Code would be added to include a join on the metabib:language_filter, so that the search languages would be included in the SQL search query.
=====Additional records added to the database:=====
A new table, metabib.language_filter, would be added to the schema. The columns of the table would be:
  *id (primary key)
  *source (foreign key to biblio.record_entry.id)
  *value (tsvector containing 008 (35-37) and 041 subfield values containing languages associated with the selected bib record.

The language_filter table would be populated via a sql script, extracting 008 (35-37) and 041 subfields from the biblio.record_entry marc field.\\

A new trigger would be added:
  * biblio.record_entry.language_filter_trigger
A new trigger procedure would be added for biblio.record_entry.language_filter_trigger:
  * biblio.record_entry.update_language_filter
A new row would be added to config.org_unit_setting_type. This would allow the MARC 041 subfield(s) to be set via the Library Settings editor of Local Administration. The value in the org_unit_setting_type would be an array containing the specified subfield.
=====Analysis of what ways, if any, this addition or change can be leveraged for future planned development=====