Have you taken a look at some of the Helm 3 proposals? One of the points that talks about this exact use case is the concept of a "library chart", which is a way to define a block of code once and import it into another chart. In your case you could then define a block of code which will spit out a set of kubernetes labels that is shared across all your charts.

https://github.com/kubernetes-helm/community/blob/master/hel...

Your other point about it being difficult to interact with the kubernetes and Tiller APIs in any other language than Go is true, though it isn't necessarily a Helm Thing. This is a Kubernetes Thing. Tiller's going away in Helm 3 so the side effect should be that Helm will be much simpler to extend.