I think the team size it’s not so much important… IMHO, the biggest and important thing its who much diversity not only in technical skills the team should be applying new cool features and handle the best way the real-world problems.
Automate such route things like mix and hex handle perfectly and use the language for programmers to use and do their jobs more fun and enjoyable.
The community born around the language needs to be inclusive no hostile, this another thing, and this always starts with a team, more people could come to language to doing contributes tough.
My principal language is Ruby and is the biggest of my new language I would like to use in the feature, by the way, is the Elixir. And they both are a good language ecosystem and community too as well, and if you analyze the javascript ecosystem and you definitely could see so much hostile environment most people stop to contribute and create their solutions, the biggest deal its create you’re transpile for Javascript, e.g Typescript, Elm, ReasonML and other and other and other, and you stop and see the big picture your community are so fragmented and the initial propose about the language does more matter.
And another example is kernel Linux is such a hostile OSS project and we see many people stop contributing because of the many dump garbage words their receive from Linus.