Revise language options for child registration

TL;DR: Solidify a list of language options on child registration to reflect languages participants generally use.

This issue covers just coming up with the list, NOT implementing the changes in the Child model & eligibility determination to accommodate it.

Narrative
As a participant, I would like to be able to report the languages my child is learning to speak, but they are not necessarily listed clearly on the sign-up form.

As a researcher, I would like to be able to set inclusion criteria based on the number of languages a child speaks, even if one or more of the languages is relatively rare.

Acceptance Criteria

• Existing languages on form have been reviewed to make sure they are appropriately named and clarified if needed (e.g., is Yue the clearest name to use for the group of dialects that includes Cantonese?)
• Language list has been cross-referenced with lab list(s) and any additional languages added (with a note about how many speakers or prevalence in conjunction with English if possible)
• A list of the most commonly used sign languages has been reviewed and a list of sign languages to add proposed (again with a note about # of speakers if possible - total and/or among English speakers, since for now our target population is parents who read English)
• Plan how to accommodate "other" languages - e.g., an "other" field with an autocomplete field (see https://baymard.com/blog/drop-down-usability) that has a really exhaustive list, plus a way to add multiple "other" languages
• If many additional languages are being added, a mechanism has been proposed to avoid making the form overwhelming (e.g., an "other" field as above to cover many of the less-commonly used languages; hiding less-commonly-spoken languages by default; moving to autocomplete field(s) entirely)

Start by reviewing the existing language options on the child registration form and cross-reference them with the lab language lists. Research prevalence for additional spoken and sign languages, then propose how to support other languages without overwhelming the form. Done means the proposed list and handling plan address each acceptance criterion.