...Then go MTL it yourself. This is a translation, not transliteration. No translator would ever say "Kappa fart", as is, in English. What you are asking for is unreasonable by any metric, I may as well just convert all the words from Hiragana, Katakana and Kanji as they are into Romaji for you to get the full experience. The fact that you don't understand that is just....unbelievable, quite frankly. If this were a series about customs, traditions, etc. then absolutely- I agree. But this is a light, rom-com series about Otaku and Idols set in modern day. But whatever, you've made clear what (twisted) idea you think translation is supposed to be, so I have no more to say to you.
I really hope that, by now, tempers have died down enough for me to be able to comment without reigniting them.
First things first: Thank you for caring so much. That's more than I can say about some other “translators”. If there's one characteristic that shines through your words, it's that you care passionately about the quality of your work.
Now.
You, as the translator, are in a position to debate whether or not the usage of the slang in this case was warranted. I do not have an opinion on the matter.
Apart from that, you are also in a position to debate whether or not it was correct. I do not have an opinion on this matter either.
What you are not in a position to debate, however, is whether or not your readers understood what the intended meaning was. For that, you'll have to ask them directly—and, from what I saw, I'm far from alone in not figuring it out until I read the comments here.
With that in mind, I hereby ask a small favour of you: A brief TL note at the end, to explain what those words mean and why they were used. For example, the translator for “Zako⁴ sensei” is rather fond of those, and I for one am grateful for them. (
The one for chapter 22 was one I particularly appreciated.)
This is, of course, assuming that you are not morally opposed to TL notes in the first place. Still, you may take or ignore this piece of advice at your discretion.