Currently the prefix `cmn` is an interwiki prefix and not and interlanguage prefix in Wikipedia: https://en.wikipedia.org/wiki/Special:Interwiki.
The wikitext `[[cmn:Foo]]` makes an inline interwiki link to https://zh.wikipedia.org/wiki/Foo instead of interlanguage linking the article with https://zh.wikipedia.org/wiki/Foo.
`cmn` is the language code for Mandarin Chinese and part of the macrolanguage Chinese (`zh`). The parts of the macrolanguage Chinese (`zh`) are:
* `cdo`: https://cdo.wikipedia.org/
* `cjy`
* `cmn`: https://zh.wikipedia.org/ the alias https://cmn.wikipedia.org/ is missing
* `cpx`
* `czh`
* `czo`
* `gan`: https://gan.wikipedia.org/
* `hak`: https://hak.wikipedia.org/
* `hsn`
* `lzh`: https://zh-classical.wikipedia.org/ the alias https://lzh.wikipedia.org/ is missing
* `mnp`
* `nan`: https://zh-min-nan.wikipedia.org/ with alias https://nan.wikipedia.org/
* `wuu`: https://wuu.wikipedia.org/
* `yue`: https://zh-yue.wikipedia.org/ with alias https://yue.wikipedia.org/
The wikitext
```
[[cdo:Foo]]
[[cmn:Foo]]
[[gan:Foo]]
[[hak:Foo]]
[[lzh:Foo]]
[[nan:Foo]]
[[wuu:Foo]]
[[yue:Foo]]
```
makes interlanguage links for all languages except for `cmn`. `cmn` is only an interwiki prefix and makes an inline interwiki link.
The prefix `cmn` should be an interlanguage prefix like the other parts of the macrolanguage Chinese (`zh`).