Which language(s) should I take?

[Zardoz]

I have taken the German RPT and achieved a Superior rating.

Given my experience, you will find the test extremely challenging unless you have perfect (college-level) reading fluency. I would say the test is strongly predictive of actual ability.

The RPTs for the other languages are not likely to be easier, so since you say that German is your strongest language, I would start there.

I eventually plan on doing most of the remaining RPT's (2-5) from your list. My Spanish reading fluency is very strong, almost as strong as German. The next strongest one for me is Portuguese, with French and then Italian last. My Italian reading ability is pretty decent but as it now stands, I doubt I would score Superior.

So my personal order would be: Spanish, Portuguese, French, Italian

The more you read in the target language, the better you will test.

I wouldn't recommend attempting an RPT if you're starting from zero. Simply because in that case, there are easier ways to obtain language credits.