Perhaps you will find Embed Discourse comments on another website via Javascript - admins - Discourse Meta more suited to your needs, as it will enable you to have discussions embedded directly under each dictionary entry.
This approach also solves the double authentication issue
Discourse auth is much more robust than a simple captcha, and it also allows for third party logins, so there is no need to use both.
And most importantly, your mission statement for the dictionary
also impacts the design for the discussion part:
- every dictionary entry will need a separate page for each language and its corresponding embedded discussion
- Discourse categories and topics will have to be designed for multilingual use from the start (categories, subcategories and tags, opt-in for select languages, optional group integration with IPPD for dictionary editors,…)
- you will need at least one native speaker moderator for each language (discussions for each translation entry will be performed in corresponding languages)
- Number of topics will potentially grow to millions (tens of thousands of dictionary entries, multiplied by hundreds of languages)
Getting the design right from the beginning is of an utmost importance, fixing the design flaws post festum is always more difficult.