Whilst Swagger Codegen doesn't create perfect libraries and some of the generators don't support all the features, once it's set up, it's just as easy to create a client for every language as it is for just one.

For example, we create multiple client libraries, HTML documentation and a partial server (so we don't have to manually write the parameter parsing and models serializers).

Another advantage is you can start consuming the API as soon as the API design is agreed, by using a generated mock server instead of waiting for the real one to be implemented.