On Wikipedia, when designing a template with a parameter that may hold multiple values, the usual solution has been to create many parameters, like so: keyword1, keyword2, keyword3, etc.

However this is often due to a software limitation and not because it's the desired design. On most modern web forms, we can enter multiple values for a single field by separating them with commas or some other character, and the software recognizes them as different values and visually distinguishes them. See for example how Phabricator does it on the Tags field when creating or editing an issue.

This functionality isn't supported at all on the template editor of the visual editor. It would be useful for designing more compact, intuitive and efficient templates.