The Min Nan Wikipedia (zh_min_nanwiki) has the URL https://zh-min-nan.wikipedia.org/ and the aliases https://nan.wikipedia.org/, https://zh-cfr.wikipedia.org/ and https://minnan.wikipedia.org/.
zh-min-nan and nan are interlanguage prefixes and link the article with the Min Nan Wikipedia. zh-cfr and minnan are interwiki prefixes and create an inline link to the Min Nan Wikipedia (https://en.wikipedia.org/wiki/Special:Interwiki). Example: https://en.wikipedia.org/wiki/Special:ExpandTemplates?title=Special%3AExpandTemplates&wpInput=[[zh-min-nan%3AFoo]]%0D%0A[[nan%3AFoo]]%0D%0A[[zh-cfr%3AFoo]]%0D%0A[[minnan%3AFoo]]
nan is the standard conform language code for Min Nan Chinese. zh-min-nan is the grandfathered alias. (https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry)
The language codes zh-cfr and minnan are only used in MediaWiki. zh-cfr was added in rSVN3742. minnan was added in rSVN4395. Both were removed in rSVN28546.
The redirects https://zh-cfr.wikipedia.org/ and https://minnan.wikipedia.org/ are not needed anymore.
The interwiki prefixes zh-cfr and minnan are not needed anymore.