One of the templates used on that page seems to use that link internally: https://fa.wikipedia.org/w/index.php?title=%D8%A7%D9%84%DA%AF%D9%88:%D8%A8%D9%87_%D8%A2%D9%84%D9%85%D8%A7%D9%86%DB%8C&action=edit (search for آلمانی)

I haven't investigated much since the RTL text makes it difficult for me to understand the syntax

I am sorry for the difficulty. I tried to replicate in a non-RTL language but wasn't successful.

As for the link, I'm afraid you are not correct. That template links to [[زبان آلمانی]] not to [[آلمانی]] but the WhatLinksHere counts pages containing it towards the latter rather than the former.

The cause was in the [[ https://fa.wikipedia.org/w/index.php?title=%D8%A7%D9%84%DA%AF%D9%88:Lang&diff=prev&oldid=15328806 | use of {{#ifexist:...}} in one of the sub-templates ]].

When #ifexists is involved, it sounds like T14019