Knowing lots of languages helps. But is more important to understand the paradigms and reasons behind the existence of those languages. Also, be able to evaluate what can be used safely by your own team. Is more important for a CTO to have a solid understanding of OOP and arhitectural patterns, understand the concepts used in designing large systems, understand DDD, but also have a good understanding of functional programming. At least high level knowledge.
Understanding data persistence strategies is also important. Being able to make informed decisions between relational databases and No-SQL is also important. However, detailed knowledge of any of those things is not needed. What matters is to be good in one field, at least and read a lot about all that is out there. Is a lot like someone knowing kung fu, and someone knowing about kung fu. If you don't fight, you don't need to know kung fu. But you do need to know about it if you are involved with fighters.