Taxonomy term name as contextual filter for view
The Term name converted to Term ID filter looks to be missing for D8 Views. 

One site-builder workaround, is to add a Relationship, Taxonomy terms on node then to add a Taxonomy Term: Name filter to Contextual Filters using the aforementioned relationship. Checking the Specify validation criteria checkbox, set your Validator to Taxonomy term name &amp; check the appropriate Taxonomy to filter on.