Translation is not easy, the difficult part in translation is different for those who are native JP/KR and those who are native EN.

Misunderstandings do happen even when speaker/listener are both native EN, for e.g. But that happens less often than when someone is not native.

So the main challenge for a native EN translator translating from JP/KR is to ensure that they understand the source's context, nuance, and meaning accurately. Phrasing it in the 1st language with the intended nuance is much easier/quicker because you have the vocabulary.

For a native JP/KR speaker who is translating to their 2nd language (English), understanding source context and meaning is the easy part. The challenging part is phrasing it in a way that native speakers will correctly understand the intended meaning.

Putting aside the intrinsic difficulty of doing translations between languages that are very different and do not have direct equivalents of words, translating to a 2nd/3rd language is hard because not only must you have a good vocabulary/grammar, you also have to be aware of how

subtle nuances for words in the language that you are translating/interpreting to will affect how it is understood. In other words, natives may very well read the meaning of your translation completely differently from what you intended.

It is not easy for non-natives to "hear" how natives take things, and to translate in both directions, cultural understanding of how both languages are used is also required. Extreme care and thought is required.

All translators know that this is not easy.

If you are a native EN speaker feeling superior enough about your own language skills to tell non-natives that they have "bad English", I would like to hear you speak Japanese or Korean. But perhaps before you learn those languages, you might try learning some manners first.