[int_19h]

It is (was?) the default for XSLT and XQuery, if we're talking about something relatively mainstream. Beyond that I can think of Dylan and REBOL.

[capableweb]

CSS is probably the most mainstream language allowing dashes in names.

[int_19h]

Depends on whether you count all the serialized data on the wire or not; if you do, it's probably XML. ~

But I think OP meant programming languages, not styling or markup.

[gpderetta]

Everybody forgets about shell scripts! Bash allows dashes in executable names (how it couldn't) and in function names, but not in variable names, at least not without a lot of effort.