How should a job title be translated? When you introduce yourself to an international audience and come from an non-US system, there always is an awkward moment of translating your job title into a form recognizable by the people you introduce yourself to. Here are the options I see:


using the title in your native language: completely honest, but probably not understandable by anyone who does not know the system
replacing it by the closest US title: complete localization, completely understandable, but some nuance in the function might be lost
translating in a literal way: something in-between


I'll give a specific example here (from my own system, the French one). CNRS is a research-performing organization, in which permanent researchers hold the title of chargé de recherche (junior staff) or directeur de recherche (senior staff). I usually see these titles translated into “research scientist” and “research director”, but I those terms aren’t really self-explanatory. In particular, I don't think it's clear from “research scientist” that this is a permanent position, because that term could also be used in other places for post-docs.
There's no single right answer here. You should provide the information that you think is most salient in the given situation. In your case, you probably want to say something like "tenured research scientist" or "staff scientist," as those terms normally give the idea of permanence in a way that "research scientist" or "research associate" might not.

If you are writing a CV in English, on the other hand, you could write "Junior research staff (permanent position)," as that gets your title more accurately. In this circumstance, it's probably better to go with a literal translation (or as Federico Poloni suggests in a comment below, the job title in the original language) plus explanation, rather than try to find the "closest equivalent."