translating Japanese into English (or any other language) is almost a completely different skillset then just reading/listening and understanding it.
As someone who has been doing this for many years at this point, this is 100% correct.
Translating creative media requires two key skills that you would think are obvious, but so many people prove that they actually are not: 1) Actually comprehending what is being said in the Japanese (i.e., knowing Japanese), and 2) Getting that meaning across into your own native language, presumably in this case English. So many of the people on this site and elsewhere skimp on BOTH of these skills, either outsourcing 1) to some MTL website, or insisting on working in English for 2) despite their mother tongue being Indonesian or whatever, because fleecing gullible idiot consoomers out of their USD requires operating in English.
Despite what Twitter morons would have you believe, translations of creative works like what happens here on Mangadex is itself an exercise in creative writing. If you understand what is being said in Japanese, including tone, innuendo, unspoken reference and so on, you will have absolutely no problem getting that across into your native tongue. Well, okay, maybe not NO problem... It changes from a question of "what is being said here?" to a question of "how can I make this make logical sense in English?"
This helpful graphic members of my own group have created really boils it all down:
The fact that you have gotten to the point where you can recognize this fact, that translation is not a PART of comprehending Japanese but instead is IN ADDITION TO understanding Japanese, is a good sign! As for how to get better at translating, I have a few suggestions:
A) Continue actually learning Japanese. Continue to broaden your exposure to the language. 1.5 years of study is a good start, but it's not nearly enough. If you've finished your elementary textbooks (i.e., Genki1+2, Tae Kim, etc), then now would be a good time to branch out and study through entertainment. Yotsuba is a good study tool because it not only introduces you to relatively simple language, it's BY NATIVES, FOR NATIVES. And, it's fucking hilarious to boot.
B) In the same vein as studying Japanese, you should be studying literature. Read some books. See how writing happens. You are specifically looking for how dialogue happens, so anything involving a lot of yapping will be helpful to you, but in reality you want to read things that you enjoy more than anything else. Personally, I love almost all of the
Black Library's output. I have never once touched a Warhammer 40,000 tabletop miniature, but thanks to Black Library I am a huge 40k fan, and there are some authors in there (Dan Abnett) that I have absolutely no shame in taking inspiration from. You can and probably should read some officially translated manga, like from actual publishers. I come from the porn world so I can't really speak on the SFW side of things, but I can vouch for
J18 (nsfw) being run by actual English speakers. I also work in an official publication, so my own works would count too. You can look at basically anything
head empty (nsfw) and
Sloppy Seconds (nsfw) have done, as I run that group. Maybe you're a victim of the Twitter brainrot though, and you think that official translations are all ~pushing an agenda~ and stuff, right? Well you just so happen to be learning Japanese, so you can compare the official translations with the raw Japanese if you ever suddenly feel suspicious about a particular line.