[DOC] Add new info about adding languages

[bruhnild]

Description

Related Issue

Checklist

• I have followed the guidelines in our Contributing document
• My code respects the Definition of done available in the Development section of the documentation
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes
• I added an entry in the changelog file
• My commits are all using prefix convention (emoji + tag name) and references associated issues
• I added a label to the PR corresponding to the perimeter of my contribution
• The title of my PR mentionned the issue associated

[babastienne]

Good enough