Somewhere I have seen #[multi word tag] syntax which would be more reliable IMHO. And aligned with markdown style to delimit text spans e.g. for purpose of linking.
#tag This sentence seems to start by tag unless you read it till the end when you realize that acording to some suggestions actually whole sentence is a tag#
Current solution/workaround:
If you need to use spaces for some reason (not hyphens, CamelCase, … suggested in posts above), Then Enclose multi-word key string in double brackets, i.e. create wiki link [[multi word tag]] instead of #multi-word-tag.