Ask HN: When hiring, which verifiable secondary/soft skills are a plus to you?

There is no shortage of discussions on direct tech and scientific skills every person working in a tech job should have. There is also no shortage of discussions on the kind of soft skills which are hard to verify or quantify (teamwork, personality, independence etc.).

What about non-essential skills (for the position) that are a bit more verifiable? To give you one example: Would CEFR[1] language certificates (let's say equal to or above C1 level) in multiple languages be something you look upon favourably?

[1]: https://en.wikipedia.org/wiki/Common_European_Framework_of_Reference_for_Languages