I am assuming that you are translating a manga, so I would recommend translating it into romaji and leaving a Translator's note saying that romaji and what it represents. e.g, ポン ポン = pon, pon (tear drops). A lot of Manga Editors seem to do it, so it seems to be the most common way of conveying it to english readers. for verbs that are sound effects, such as ワクワク, translate it into the verb it represents. In that case, it is 沸く, which means to get excited/to boil. In the previous example, I would recommend "tremble" or "shiver", because they are both verbs that are in present tense that are commonly associated with getting excited.
I personally would recommend that you modify the art as little as possible except to restore quality, as I enjoy reading the sound effects in kana format and imagining them. That is why I recommend a footnote, or translator's note that says the transcribed sound effect (if it's not a verb), so that english readers can enjoy the same luxury.
P.S.
For phonetic sound effects, I would leave a translators note saying for example, "fuan fuan fuan (sirens)" or "poro poro (sound of tear drops falling)"
