When hiring software engineers, should you place more weight on the expertise of the specific language or framework you are using, or overall skill and experience.
i.e. A great engineer with 10+ years of experience might not have used the Python programming language. But can likely learn it easily.
The downside I see is the temporary cost to the startup of such an engineer to learn your programming language or framework.
What do you suggest?
It depends on a few factors (some of which are both related):
If you're an early stage startup (and most at this stage have limited resources), I would recommend someone who already has experience with the specific language/framework you're building your product on.
But once you start to gain some traction and have more resources, hire great engineers regardless of their experience on your particular language/framework. Some of the best software developers I know aren't boxed into a particular language. They're generalists who are language-agnostic.