> if Turing completeness is a requirement to be a programming languageMany languages (in the formal sense) aren't Turing complete, so this certainly isn't a requirement to be a formal language. It would be odd to come up with a definition of language that excludes regular languages, for example.
TBF you did say "programming language", not just "language". But once we move from the mathematical setting of formal languages into the informal engineering setting of programming languages, I don't see why a formal concept such as Turing completeness should be the deciding criterion for what constitutes a programming language.
I think a more reasonable criterion is that a programming language needs to have at least 1) a syntax; 2) a semantics or an implementation that could, with enough effort, be given a semantics; and 3) whose primary use is giving instructions to some computational machine (Turing or otherwise).
According to this criterion, SQL is certainly a language.
If you think about it for a moment, HTML and CSS are perfectly reasonable languages as well. Their semantics, however hairy, would be given for instance terms of manipulating objects in R^2.
