[reshlo]

The text preceding that list is “if … you want a diverse audience”, which suggests they’re asking conference organisers to send personalised invitation letters to every foreigner who wants to attend, not just speakers. That could mean thousands of letters.

[ghaff]

Almost certainly not thousands given that most large tech conference attendees are North American and European. But it's totally routine for large conference organizers to provide visa letters for attendees upon request. e.g. https://events.linuxfoundation.org/open-source-summit-europe...

[Ar-Curunir]

If a person has registered for a conference (which I imagine involves paying money), it’s the responsibility of the conference organizer to provide a visa invitation letter (which can just be derived from a template; doesn’t have to be specialized), as many visa applications require such a letter. Otherwise they should refund the money and not accept applications from foreign participants at all.