It is sometimes useful to see a list of users who contributed to the translation of a project. The only ways to do it currently is to check the history of each message, which is very inefficient, or to read the metadata in the exported translated file, which is also inconvenient, because every project does it very differently.
Alternatively, one can check the list of translators for one language at [[Special:SupportedLanguages]] and then manually filter those who contributed to the project in question. Maybe the special page could allow filtering by message group. If the performance allows, such a list of translators by message group could be expanded to also offer all languages at once.
Possible solution: a Special:SupportedLanguages variant which displays translators for all languages, but only for a specific message group. A similar group-based filtering can be considered for Special:LanguageStats (which is sometimes perceived as too long/heavy, see T160902#3114186).
(For translated pages it is also possible to check the history in a usual MediaWiki way, but that is also not the most efficient thing. For file-based message groups)
See also: T56279: Statistics for all translations in all languages in a site