What is the difference between Lubuntu and Xubuntu on the basis of development communities?

Solution 1:

There is the wider Ubuntu community, and within that community smaller communities.

The Lubuntu team can be considered of team members (https://launchpad.net/~lubuntu-members) and those helping the team (that may become members themselves in due course).

The Xubuntu team likewise consists of team members (https://launchpad.net/~xubuntu-team) and those that may themselves become members in due course.

Some Ubuntu community members help all teams, or help some (be it their favorites, or those in need of their skillset, or whatever they decide).

How do you become a member (see https://wiki.ubuntu.com/Membership), you apply, but you'll be expected to show sustained and significant contributions (https://wiki.ubuntu.com/Membership/NewMember).

Becoming a member of a flavor is the same including need to show sustained and significant contributions so I won't include links as each flavor has their own slightly different page that is essentially identical. When you become a member of a flavor (##Lubuntu, Xubuntu, Kubuntu) includes Ubuntu membership (if not already attained, ie. Lubuntu team members are not separate from the Ubuntu community as a whole, just a group within the wider group which includes Kubuntu, Xubuntu, Ubuntu-MATE, Ubuntu-Studio, Ubuntu-Budgie, Ubuntu-Kylin [all flavors]).

The community support the 'universe' repository, which is where all flavor packages are found. Long term support (LTS) flavor releases have generally only three years of support compared to the 'main' repository which is for the most part maintained by Canonical employees (having five years of support for LTS release, longer via use of ESM) https://help.ubuntu.com/community/Repositories/Ubuntu

I've only used Lubuntu and Xubuntu as examples because you mentioned them in your question, the same applies to all flavors & smaller communities within the wider Ubuntu community.

--- Later amendment

##Please note my wording (where I marked with ##) applies specifically to Lubuntu, Kubuntu & Xubuntu or the older flavors where full Ubuntu membership requirements must be met for flavor membership. The newer flavors (Ubuntu-MATE, Ubuntu-Budgie, Ubuntu-Studio.. ie. those that start with Ubuntu-) can actually have slightly lower standards, as Ubuntu Membership is a second separate application. As many of those members have met the significant and sustained level anyway the difference may only be formality (but there is a slight technical difference between ?ubuntu & Ubuntu-? flavors)