Ada with the Ravenscar profile enabled is a good choice for such scenarios. Together with a real-time operating system it allows you to satisfy hard real-time guarantees. As you certainly know, though, hard real-time constraints require hardware validation.
Yea, for a lot of requirements hard realtime isn't necessary and at least some older linux systems can be tuned to remove almost all jitter giving very good 99.9th percentile figures. I've even seen it done with zero alloc java
Some domains might state a worst case for a single transaction or percentage of transactions that definitely exceeds what can be achieved here