Thank you Fuistes for picking up this manga! I commend you for your efforts. There are a lot of small details that are hard to describe in text, but here are some major translation things I noticed while reading:
On page 3/37, "Please everyone, don't put those faces." should read "Please everyone, don't put on those faces." In the same way you put on a mask, you put on a face.
On page 4/37, "The people and the country still" should read "the people and country still". When you use a conjunction ("and"), it sounds awkward to repeat the definite article ("the").
"
On page 4/37, "Ohh... What pleasant surprise." should read "Ohh... what a pleasant surprise." This is just a weird one-off thing that doesn't match most of the rest of English's grammar rules (English has a lot of those).
On page 4/37, "Never thought that in my last moments, my eyes can see you again..." should read "I never thought that in my last moments, my eyes could see you again..." Since the king is talking about himself, the verb should start with "I". Because he is talking about something he thought, not something that is actually happening (even if it is actually happening, this is how you handle things that are thought / wished / possible), "can" should be replaced with the subjunctive "could".
Page 5/37, "for the sake of this world and his people" should read "for the sake of this world and its people". "World" isn't a gendered down, so you use the neuter possessive pronoun "its".
Page 5/37, "I believe that is a greatest achievement that needs be rewarded." Unfortunately, I can't properly explain why this is awkwardly worded, but it is. I believe it would read better as "I believe that this great achievement should be rewarded.
"Page 5/37, "There is anything that you wish?" should read as "Is there anything that you wish for?" This is just the correct word order for questions in English. Other examples (not in the manga) of this word order include "Is there anything you want from the store?" and "Is this what you had hoped for?"
Page 5/37, "I grant you anything that you want" should read "I will grant you anything that you want". Because she is talking about something that is going to happen in the future, "I grant" should be in the future tense, "I will grant.
Page 6/37, "there is no doubt you need be rewarded" reads better as "there is no doubt you need to be rewarded". That "to" can technically be left out and inferred through context clues, but it sounds a bit awkward here.
Page 6/37, "In the way I lived, there's nothing that I'm ashamed of." is just very wordy. The same thought can be expressed as "I lived shamelessly."
Page 6/37, "I was only a man born in a farmer's house that later train his body to be a mercenary who eventually become half-man and half-god when they give me the title of divine knight, and finally I build a country." is overall too wordy, and uses the present tense, even though these are past events. Further, you can't turn your body into a mercenary, but you can turn your body into a mercenary's. I believe "I was only a man born into a farmer's house who later trained his body into a mercenary's. I eventually became a half-man and half-god with the title of divine knight. I used this power to build a country." would work better.
Page 6/37, "I'm proud of given my life for the sake of the country and his people." should read "I'm proud to have given my life for the sake of the country and its people." Country is not a gendered noun, and you should thus use the neuter pronoun "it" (in this case, the possessive "its").
Page 7/37, "If I can... Instead of a king, I can be a military man, then--" should read "If I could... Instead of a king, if I could be a military man, then--" Once again, since he's talking about a hypothetical, "can" should be replaced with the subjunctive "could." I further changed the wording slightly to represent how people actually trail off in thought.
Page 7/37, "If I can... devote my whole life to being a military, then..." I don't understand why this is hear. Maybe the original text had the king repeating his statement with some variation, but as is, this is just useless repetition. It can be deleted. Maybe, if you wanted this repetition to add to his speech, you could use "If i could... devote my whole life to the military, then--"
Page 7/37, "I wish... I want to be reborn once again." should read "I wish... to be reborn."
Page 10/37, "There is no doubt about it; this was thanks to the goddess power." should read "There is no doubt about it; this was thanks to the goddess's power." Because the power belongs to the goddess, you should use the possessive "goddess's".
Page 10/37, "¡But we did it, Selena!" should read "But we did it, Selena!" English doesn't use the inverted exclamation or question mark at the beginning of sentences.
Page 11/37. This page uses both the inverted question mark and exclamation point at the beginning of a sentence. English uses neither.
Page 12/37, "It's she gone." doesn't make any sense. It should either read "She's gone." or "Is she gone?". I'm not sure which is closer to the original, but those are the two that make sense in context.
Page 12/37, "Also, the smallest movement I make, I feel sleepy and can't pronounce words either." just reads incredibly awkwardly. I believe this could be better stated as "Further, the smallest movements make me sleepy. I can't pronounce words either!"
Page 13/37, "... then I can resolve to live in this body." should read "... then I can muster the resolve to live in this body."
Page 14/37, "The source of the magic it's the mana, although in reality that is a representation of the ether." reads awkwardly. "Mana" describes "the source of magic", so it should be put in parenthetical commas. Further, "although in reality" is redundant. I believe this would read better as "The source of magic, mana, is actually just a representation of the ether."
Page 14/37, "Whoever it can control that, it means he has obtain the power of god." also reads incredibly awkwardly. I believe the same thought can be expressed as "Whoever can control it may obtain the power of god."
Page 14/37, "From now I have to gain practice." should read "From now on, I have to gain experience." You can't gain practice, but you can gain experience.
Page 14/37, "The magic stone beast..." should read "A magic stone beast..." There are tons of different magic stone beasts, and this is just one of them, so you should use the indefinite article ("a").
Page 15/37, "¿¡It's she floating!?" should either read "Is she floating?" or "She's floating!" I'm not sure which is closer to the original meaning, but your translation doesn't make any sense. Again, English doesn't use the inverted exclamation or question marks.
Page 15/37, "Maybe, I seeing things...?" should read "Maybe I'm seeing things?" The comma is unnecessary, and "I seeing" isn't a valid verb, but "I'm seeing" is.
Page 15/37, "Everything, it's all right Inglis. Come with mom, to seek shelter" should read "Everything is alright Inglis. Come with mom to seek shelter." See previous points as to why this is wrong.
Page 15/37, "In my past life, I never heard about such being..." should read as either "In my past life, I never heard of such beings..." or "I never heard of such beings in my past life..."
Page 16/37, "Preferable a extremely brutal and powerful a monster worth to be defeated." reads very awkwardly, and you used use "an" instead of "a" for words that start with vowels. I believe this would read better as "Preferably an extremely brutal and power one, a monster worth being defeated."
Page 16/37, "Are you waiting for us!?" should read "Were you waiting for us!?" The waiting happened in the past, so this should be in the past tense.
Page 18/37, "Yes, here you have it." just doesn't sound right. It would probably be better to say "Yes, as you can see." or just "Yes!"
Page 19/37, "That gem's glow, It's a condensed mana's power. That thing is it's a terrible menace for the society." should probably read "That gem's glow... it's the power of condensed mana. That thing must be a terrible adversary!" I changed the meaning slightly, but i believe it fits better.
Page 20/37, "The best it will be if i deal with him" also doesn't make any sense. Try "It would be best if I could deal with him."
Page 20/37, "Kris! be noising it's bad." also doesn't make any sense. Try "Kris, stop being so loud!"
Page 20/37, "For the future of these childs" should read as "for the future of these children,".
Page 20/37, "with magic stone beast" should read "without magic stone beasts".
There are more, but I unfortunately won't have enough time to go through the rest for quite a while. I can go more in depth on any one of these later though.