You may want to consider looking into go modules. It works much the same way that cargo does for rust and you won’t need to worry about GOPATH for most cases.
len("föö") = 5
should instead have returned len("föö") = 3
I submitted a pull request, https://github.com/christianscott/levenshtein-distance-bench..., that fixes these issues in the Go implementation. old: 1.747889s
new: 1.409262s (-19.3%)