Insert multi fields data

hi,
I am looking for a solution that inserts translated data into multi fields for multi-language

Welcome!

This might help: Best practices for multi language search and index

I am using (per field ) pattern that returns title_fr and title fields but I have title property in my source(nest or .net source code ) and title_fr must be mapped to title.
i am looking for away to doing in nest.

Multi-fields allow an individual field on the input document to be analyzed and indexed in multiple different ways to serve different search needs.

Based on your posts, it sounds like you already have the translated data for multiple languages e.g. French title title_fr, and wish to also index these into Elasticsearch along with title, perhaps setting up different analysis for each. If I've understood correctly, Multi-fields isn't what is needed here but instead two separate input fields on the document, title and title_fr.

thanx for your reply.
My problem is getting field (title_fr or title_nl or ...) as title property, my support language list is dynamic and I create a field for each language with ELK Mapping and I can set the correct language field with pipeline and use it in a search query but I don't know how to get for example:
title_fr as title or title_en as title or ..... based on user default language in result

You could probably use script fields to return a specific _source field as a field value. Note that this will return the field in the "fields" property for each hit and not the "_source".