Related to T911, in the list of projects at https://phabricator.wikimedia.org/project/query/all/, I noticed a few things:
- Most of the projects (migrated Bugzilla components) use hyphens.
- The names of release projects (e.g. "1.19.x release", migrated from Bugzilla's Target Milestone field) contain spaces. The corresponding hashtags contain underscores.
- Projects such as "Browser_Support_Apple-Safari" (migrated from Bugzilla's Web browser field) use a mix of underscores and hyphens.
- There are other project names (e.g. "WMF Design") that use spaces as well.