Except that both languages and "application architectures" are, so as to speak, both based on usefully constraining the set of valid programs.
Sorry I don't understand what this means. If you design a data schema that can't scale no language selection, amount of clustering, sharding, money or associated BS is going to be of much help... this is just reality.
This is true, but it does not lead to what you are claiming. A data schema (in a very general sense that goes beyond relational schema or XML data schema or whatever) might or might not scale (either by poor design choice, or by design).
But that schema will depend on specific concepts and assumptions that will be best realized with a specific family of technologies (or even a single one.) It would be possible (but very hard and stupid) to try to implement a relational data schema with a document-oriented database. And it would be very painful to implement a flexible document-oriented system using a RDBMS.
A good design of each type of system would achieve most, if not all of the requirements desired for such a system, but they will make a significant number of platform and language support assumptions.
Design and architecture are not some ethereal things up in the clouds; they are meant to be rooted on very specific language and runtime constrains.
Only when machines become smart enough to do the designing will this ever change.
And since that is an undecidable problem, we know that will never occur (not without heuristics and constant human
intervention, validation and verification.)
Computers can do a lot on the margins but ultimately if you want scalability and performance in a non-trivial problem space YOU will have to work for it.
Yes, YOU have to work for it... using the appropriate levels of abstraction (be them run-times, frameworks, language features or any combination thereof.) Architecture and design are about constrains, about constraining the number of ways entire systems can be put into place within limited resources. That constrain alone dictates what language and platform features make architecture and design feasible.
What does constraint validation have to do with scalability and concurrency?
I'm not sure what the OP intended by "constrain validation", so I would present my own interpretation. A constrain or set of constrains will indicate how much scalability or concurrency you need. Those constrains then become vital for describing the means for testing, validation and verification (after all, a requirement is only valid when it is testable and verifiable.)
I could architect a large-scale e-commerce site with strict fault-tolerance and consistency requirements. Great. Then, I can, in theory, implement it in assembler, or C... or with a higher-level language and platform.
Similarly, I can architect a distributed operating system. I could implemented in Java or natively compiled BASIC... or I could do it in C/C++.
Proper architectures for each problem will prescribe the constrains of the design (and the means for verification and validation), and each will be better served by specific languages and tools.
Any non-trivial architecture will have a direct dependency to a set of language features. And any set of language features will have a relation of economic feasibility to families of problem domains and related architectures.