(A TODO was added in rMW2f64d0087d3af3de12855cba0c1057309f1049d5 to allow - to be used as an access key, as part of [1] that todo comment was removed, filing a task so it doesn't get forgotten)
In general in mediawiki messages, setting a message to - disables it. But, in the case of access keys for links, that might not be desirable behavior - instead, - should be treated like any other character and support for use as an access key
[1] https://gerrit.wikimedia.org/r/c/mediawiki/core/+/661693