The two appear to fairly often be used to mean roughly the same thing; particularly, "license" seems to often be used as a more specific version of "legal". However, there are license-related questions and certainly licensing-related questions that are not legal questions per se. Take for example Why do you have to be 18 to be a Volunteer Examiner?, which asks about the US amateur radio license exam system; while the act of licensing is a legal matter, the license exam system can be discussed outside of that legal context.
Abstractly, I think tags should be defined in a way which leads people guessing how to tag their questions to usually guess correctly. (For example, a tag should not be “X but not Y, because we have a tag for Y”, because a new questioner is likely not to know what tags exist.)
Trying to define these tags in the most straightforward way which still leaves them distinct, this is what comes to mind:
license is for questions about getting, having, renewing, etc. your license, or about what you can do with a given class of license in a given jurisdiction where multiple classes exist.
legal is for questions about the regulations as written and what is permitted by them.
For a example, a question about how to get a license is a license question, but not very much a legal question because it's not about what is permitted but what is normal procedure; asking what the law is is not to the point unless you're trying to argue with bureaucracy.
There are certainly possible questions which can reasonably be tagged with both, but not most of either type of question, and that's what we should be aiming for.
I feel the difference between the tags should be the following.
license covers questions related specifically to licenses and licensing of amateur radio stations but which are not answered by a reading of applicable legislation or precedent-setting legal cases. For example, this might cover:
- the aforementioned question
- Would I still be a valid volunteer examiner? (because it is about licensing, as well as about membership in an organization)
- What is the body of knowledge the U.S. written exams test? (because it is about license exam questions specifically, which insofar as I know are not legally specified)
- What is the procedure to obtain an amateur radio licence in Australia? (because it is about the act of becoming licensed; obviously this might be borderline)
legal covers questions that are specifically answered by the relevant legislation, or by precedent-setting legal cases in case of ambiguity. This might for example be (because all of these should be answerable by reading the appropriate legislation, including international regulations, and/or any precedent-setting cases):