The relative stability of different procedural languages

I'm facing a particular task for which I need any procedural language
but PL/PgSQL. I can't use PL/PgSQL because it doesn't allow me to use
local variables such as new and old from a dynamic command.

However, I've been unable to find any useful information on the
stability of each particular procedural language. I've seen suggestions
for creating a PL comparison matrix, but, short of such a matrix, I
couldn't even find essential information regarding the vitality and
stability of the various PLs.

I'm comfortable with both Ruby and Perl, but wouldn't mind brushing up
a bit on my Python. I'm also comfortable with PHP but have to say that
the idea of running it within Postgres doesn't appeal to me very much.

So, how to the different procedural languages stack up against each
other in terms of stability? After all, adding a language that could
cause random segfaults or huge memory leaks is simply not an option for
a production DB.