You can add articles to Wikidata items by going to the items and adding it manually, by going to the item, entereing the language code and the article name.
However, even when that is done, the articles on the Atikamekw Wikipedia don't show any language links, and the other languages connected to that item don't link to the Atikamekw Wikipedia. Example: https://atj.wikipedia.org/wiki/Manawan_sipi, which is connected to https://www.wikidata.org/wiki/Q15122970, so there should be a link to Atikamekw on https://fr.wikipedia.org/wiki/Rivi%C3%A8re_Manouane_(La_Tuque), but there isn't.
Also, it's not possible to add interlanguage links (i.e. connect an article to a Wikidata item) the quick way, by clicking the "Add links" link under the "Languages" header in the sidebar (you can enter the language, but the "Article" input field stays grayed out and uneditable).
I suspect this is related to T167720, since that step – understandably – seems not to have been taken when the wiki was created, but I'm not sure.