Feature summary (what you would like to be able to do and where):
translating a link that exists in the source language but not in the target language should create an interwiki redlink if the target wiki has that template.

rather than [[missing link]] it becomes [[missing link]][tg].

e.g. on the english wiki:
{{ill|Guilde française des scénaristes|fr|Guilde française des scénaristes}}

https://en.wikipedia.org/wiki/Template:Interlanguage_link

Use case(s)
You are translating a page from a source language to a target language, but the target language doesn't have certain linked subject yet.

Benefits :
Like regular red links, they encourage expansion, but they also point out where one could get quality references and subject material as well, for free.

It also encourages more translation.

It also ensures that the redlink refers to the correct subject/helps reviewers check the translation is correct.
With technical term translation, there such doubts can arise quite a lot.