@Pandawanka
Yeah no that is just nonsense. It's not even frequent lingo... it's gonna go the same way 99.9% of all other internet insults go and be used for at most half a year before being forgotten and having to be looked up on Urban Dictionary or KnowYourMeme.
As a translator you simply don't use such stuff except, as I said, when it is actually part of the characterisation. In manga, this can mostly be seen in gyarus or net gaming-related characters who will be all "lul" and "omg" - which in that case is fitting because not only are those terms way better known and more likely to stay for longer, it befits the character. In this dialogue however, the sudden appearence of simp was a foreign object and unfitting.
@phil777
As a translator: yes language is ever-evolving and changing. But no, that does not at all mean that every single dumbass flavour-of-the-month word becomes a part of a language's vocabulary. The vast majority is never used by more than a small group, and disappears as quickly as it appears. Go to Urban dictionary, flip through the entries, and then think about how many of those you've never heard / never heard in the context it was being used. Hell, I could take last years edition of the youth vocabulary dictionary (something that actually exists where I am from) and go to a highschool class, show it around and I bet you that at least two thirds of the entries will be something nobody in class will ever have heard and sound strange and dumb to them. I know it, because I've done that before. And we're talking about a language that is way more regionally contained than English and thus should have way less variety in trending vocabulary.