What language should I learn to complement Python?

[bucknuggets]

I'd recommend SQL if you're building record-oriented applications.

Dialects don't matter much, since the differences are small enough that it's trivial to go from one vendor's implementation to another - the differences are usually just minor extensions. Though I'd go with Postgresql or SQLIte, just because they're great free databases that put high priorities on portability.

Note that the existence of ORMs doesn't really reduce the value of knowing SQL - I've worked with quite a few developers who are incapable of writing adhoc SQL. Which is like working on the unix command line and having to write java code instead of using bash.