Currently all interwiki links are marked with the class `extiw`. External links that are not interwiki links, are marked with `external` (and are visually made distinct using the external link symbol. Unfortunately the interwiki links can generate both true external links and links that falls within the same family (for us WMF links).
For end users, it is likely a good idea to differentiate external and internal wikilinks better. To avoid confusion.
* Any link that links 'off site' should be marked with the class external, wether or not it is generated with the extiw markup or the external link markup
* Any link that falls within the same wiki family (WMF properties) should not have the external link symbol
* Any interwiki link that does NOT fall within our wiki family SHOULD have the external link symbol
Links in the same family share SSL and CORS concepts, this is an additional reason to make expectations of the user match these concepts.