In practice
Every version must point at every other version, including itself. A one-way reference is ignored.
Add an x-default for the page a visitor should land on when no language matches, and keep hreflang and canonical consistent with each other.
Why it matters
Without it, engines choose a version for the user and often choose wrong, sending a Turkish visitor to an English page.
It also stops the two language trees from competing with each other as near-duplicates.