Thanks for the additional context, Felipe!
Adding a language attribute for titles is not something that we’ll be adding. In your use case, only adding the title in multiple languages is a somewhat misleading practice, since the translated title is only available in the metadata. Thus, if a metadata user is looking for content in Spanish, French, and English and you’ve registered titles in all three languages within the metadata, but then there is no full-text in, say, French and English, we would argue that more harm than good has been done to that metadata user who was attempting to discover the content in those other languages. That metadata user would retrieve the metadata title in multiple languages to only find out that the full-text content itself was not available in those other languages. That’s not best practice.
Warm regards,
Isaac