@Fuistes
Concerning the suggestions on how to write better, I think
@Saklas already gave you a very detailed one.
What I'd like to recommend you is
Grammarly. It's likely the best English writing assistant out there. I'm always using it when writing English texts (English isn't my native language, either) and I can tell you that it highlights the mistakes very accurately.
What I also really like about this extension/app is it's free. There is also a premium version with further features. But the free version already tries to correct all the mistakes in your texts. The premium version further gives you tips on how to improve "the structure" of your text to make it easier to read and more professional. As these are not really mistakes, the free version is actually enough if you only want to correct potential mistakes, especially when you're translating manga.
Maybe 2 things to note: while using the free version, you might sometimes see "passive voice misuse". They're not mistakes, even though they seem to be. And you might want to check the settings (just click on "Goals" or "Adjust Goals") and use "General" for the audience and "Informal" for the formality. I think it depicts the type of texts in mangas.
If you're not sure which sentence structure you want to use, you can also try to use DeepL. Just type your text in Spanish on their website and see the English translation. Or type the English text and see the Spanish translation. This will sometimes give you a rough idea of what to change. DeepL is probably the best translating app out there (although I can only assure it for English-German translations). Here's a link if you're interested: https://www.deepl.com/home
I hope these two apps will help you!