Since I'm not doing lowlevel stuff, for me it would be a statically typed language that has a typesystem so powerful that it never gets in my way and lets me express all constraints in types that I need for my domain (so it must be a value-dependent typesystem or similiar). In addition, the syntax must be terse so that it's easy to define (business) datatypes and mappings easily, so that someone can come in and read those definitions quickly and understand the domain.

And then one feature that I like which few languages support are some kind of contexts. Scala does this really well for example, but even in Scala it could be improved.

What I mean is that code that looks the same can mean different things in different contexts. The typesystem then ensures that it cannot be used wrongly though.

An example would be how "5 ± 3" can mean different things depending on the context, such as "1 or 8" or "mean of 5 with variance of 3" (in statistics).

Without such a feature it's hard to translate thoughts into code as easy in certain domains.