Okay, so I've attempted to play the 5.0.2 version from the start and wrote down any spelling mistake, punctuation error and other faulty grammar I could find. Currently, I almost feel like the weakest part of the game are the dialogues, so I really wanted to do you a favour and improve that for the main release.
I've tried to leave out corrections that are based (too much) on personal preference, but in some cases I just suggest an altered sentence. I don't try to be mean, I just want to show my love for the game by making it a bit better on a textual level, as far as I can do anything about it as non-native speaker.
Because I've already written down a vast amount of mistakes, I'll just present everything up to Crestlight City (including the Gym and Blackleaf Woods) for now. My suggestions and/or reasoning are in italics:
---Soltree Town---
Sign: text is not centered like other town signs.
Mom: You should head over to Prof. Pinewoods lab
-> Prof. Pinewood's LabMom: Come and get your first Pokémon!
-> Go and get your first Pokémon!Dad: Prof. Pinewood's Lab is in the north part of Soltree Town!
-> northern part ofAssistent @ Pinewood's Lab: Take these with you!
-> Take this with you! | You get only 1 potion from him.Rodney (after losing battle): Wow! I won! Dont worry about it!
-> Wow! I've won! Don't worry about it!Rodney (after battle): I dream of being one, one day!
-> being one of them | He refers to the Elite Four.Mom (giving running shoes): These will surely help you get to where you want to go faster!
-> These will surely help you to travel a bit faster, everywhere you go!---Route 1---
Youngster @ Headbutt tree: Hey, do you know about this kind of tree on my left?
-> The tree is on his right, though.Youngster @ Headbutt tree: its possible that a Pokémon will fall down
-> it's possibleGirl (when delivering the letter): Oh, what`s that?
-> what's | wrong apostrophe---Mossy Town---
Guide (about the quest area): People who havelost something and need...
-> have lostKid (northwest building): My mom works at the Pokécenter.
-> Dad talks about Poké Center. | I like consistency. ^^Keira (when picking her up): Well, Id better go get my Pokémon.
-> Well, I'd better get my Pokémon.Youngster @ Poké Center (after delivering his letter): Sorry, but now I need a bit time for...
-> now I need some timeStairway @ Keira's house: I think you shouldnt go into Keira's room...
-> I think you shouldn't---Serpentine City---
Sign: The Garden of Rikoto!
-> The wiki says "the rose garden". If that was an addition, it should be there as well. 
Woman @ Poké Center: Hello, i'am staying here, because i lost my three kids, they are running through the city, but i can't find them... [awkward space] Can you help me finding them?
-> I'm staying here because I lost track of my three kids. I think they are running through the city, but I cannot find them...Woman @ Poké Center (selecting "no"): Oh, i see, you have no time...
-> Oh, you have no time? I see...Woman @ Poké Center (selecting "yes"): Wow, thank you so much, i hope you can find them!"
-> I hopeDonna's father (before battling Donna): Tell you what: if you can beat her and show me [weird space] the Gym Badge...
-> You know what? If you can beat her, etc.Gatekeeper (east): You should always take enough Poké Balls with you so that you can always catch the...
-> You should make sure you have enough Poké Balls with you. Doing so, you can always catch the... etc. Donna's father (after winning): Oh! I see that you beat my daughter!
-> Oh, I see you have triumphed in the battle against my daughter! | Just for some variety.Donna's father (after winning): It allows you to cut down small trees in the way and sometimes other objects!
-> Rephrase to "It allows you to cut down small trees and other objects blocking the way."Donna's father (after getting HM01): HM01 is CUT. You can cut things like bushes and webs.
-> Maybe: HM01 contains Cut. You can cut down things like bushes and small trees, but I remember it's also effective to cut the thick webs Spidox spin in Dullfern Forest!Keira: This is an EXP Share!
-> Item says "Exp. Share"Keira: If you give this to one of your Pokémon, it will gain EXP without participating in battles!
-> experience | It's more clear I think.Keira: Now, Im heading over to Serpentine Garden to train my Pokémon.
-> I'm heading toGatekeeper (north - to Dullfern Forest): Every Forest in Rikoto has his own features, different Pokémon and different colors.
-> Every forest in Rikoto has its own charms, be it their distinct atmosphere, their unique Pokémon, or their hidden mysteries... | something more interesting I hope. 
---Serpentine Garden---
Bug Catcher Lillian (after battle): I love Bug and Fairy-type Pokémon, and Pixwee are both of those types!
-> Sometimes, it's unclear if a plural form is used for Pokémon. I would say "Pixwee is both of these types", since she has only 1 Pixwee.Youngster Jerome (after battle): Sometimes, you can find items that can't be seen by looking at rocks and empty patches of grass...
-> Try scanning an area for lone rocks and empty patches of grass. Sometimes, you can find items there that cannot be seen!Donna: I come here all the time to relax after my Gym battles. It's very relaxing!
-> Twice relax, I would suggest: I often visit the garden to relax after my Gym battles. / It's very uplifting!Rodney (before the Gym, after battle): I enjoyed it.
-> Wasn't that Keira's line after defeat?Rick (in front of the Gym): ...so that I can compete in the Rikoto league so that I can defeat Rikoto Champion!
-> repetition | So that I can compete in the Rikoto League, and ultimately, defeat the Rikoto Champion!Rodney (after Rick): Wow That guys rude... We'll show him, right? Well, I had better go heal up my Pokémon and also go to Crestlight City.
-> Wow, that guys is rude... We'll get him later, right? Anyway, I'd better heal up my Pokémon and go to Crestlight City as well.---Serpentine Gym---
Gymdude: Then you have to know that you are only allowed to battle the Leader with the maximum of the same amount of Pokémon as the Leader. [weird space] If you have more in your party, you have to choose them before!
Gymdude: She is using three Pokémon for her battles, so you can choose up to three as well!
-> Those lines can be combined! | First, you have to know that you're only allowed to battle with the same amount of Pokémon as the Gym Leader. Donna uses three Pokémon, so you can choose up to three Pokémon as well. If you have more Pokémon in your party, you have to pick them wisely.Gymdude: The Gym here is like a maze of rose hedges and trees, so be carefull that you didn't get poisened on their thorns.
-> The Gym is a maze of rose hedges and trees, so watch out for any thorns.Gymdude: But I'm sure you will find your way to Donna... Or maybe not, haha!
-> Errr? I think it's better to remove that "maybe not" part. 
Gymdude: Maybe this will help you beating her:
-> Maybe this will help you to beat her / Maybe this will aid you during the battle.Lass Vinal (after battle): Hmm try your best...
-> Maybe "Hmm... Try your best..." I liked that pause after hmm, but I think it's more effective with the dots.Gymdude (after winning): Wow. What an amazing battle! You won, so I engraved your name on the statue!
-> maybe change "you won" to "you managed to win" to have some variety. ^^---Dullfern Forest---
Rick: I see you won the Gym badge... Ha!
-> I see you've earned/managed to get the Gym badge... | Just a suggestion again.Rick: You're most likely gonna get attacked, though.
-> Most likely you're gonna get attacked, though.Bugcatcher Alan (after battle): How many do you think live here?
-> How many Pokémon live here, do you think? / Do you know how many Pokémon live here?Commander Scarlett: Who are you? Don't you know it's rude to listen to others private conversations...?
-> You're rude, eavesdropping on private conversations!Male Grunt: We'll take care of them
-> I'm singular thanks Youngster Jerry (after battling Team Solar): They are gone? Thats fine. I was totally frightened...
-> Just, fine? It should be SUPERB UNBELIEVABLY AWESOME! Or maybe change it to "That's a relief! I was totally frightened by them..."Youngster Jerry (after winning): WOW, now i know why you aren't frightened!
-> Wow, now I know -etc.Youngster Jerry (after battle): Who were those people and why were they in such uniforms?
-> Who were those people, and why did they wear such uniforms?PkmnRanger Mae (after battle): It's said that there's a Legendary Pokémon living in the temple...
-> no need to capitalize "legendary".PkmnRanger Rudy (before battle): The temple is impressive.
-> Perhaps: "The Earth Temple is impressive."---Route 2---
Keira (before battle): Now I'm going to take on the Crestlight City Gym Leader! Lets do our best!
-> Let'sKeira (before battle): The berries on it are called Apricorns. They come in all these different colors!
-> The berries of it / They come in all different colors!Keira (after battle): You see, there's a man in Orshore Town that can turns these Apricorns into special Poké Balls!
-> You know, there's a man in Orshore Town who can turn these Apricorns into special Poké Balls!Keira: These Poké Balls are special because he makes them by hand.
-> Ehm, they are special because of their unique qualities, right?Keira: Each different-colored Apricorn makes a different kind of Poké Ball!
-> What kind of Poké Ball you can get depends on the colour of the Apricorn.Keira: Well, Id better go!
-> Well, I'd better go!Youngster Kirby (after battle): Good luck collecting Badges!
-> Good luck (with) collecting the badges! | I think it sounds better, but I'm not sure about the proposition...---Crestlight City---
Dude (westernmost house): when I'm done with my research here, /weird space/ I plan on going to a city...
-> When I'm done [...] I plan to go/move to a cityFisher (north): Theres nothing like a good time for fishing.
-> There isn't anything like a bad time for fishing! | I think that's what is meant?Fisher (after getting the rod): I'm glad to help Trainers see how fun fishing can be!
-> I glad to help trainers understanding the fun side of fishing!Gymdude: But, if youd like, you can go and retrieve him from Blackleaf Woods to the west of here. He's out training.
-> Reverse info and rephrase: "Damon went out for training. If you'd like to challenge him, you can try to find him in Blackleaf Woods, here at the west side of the city.Woman (northwestern house - after getting Dusk Balls, re-talk): It will help catch pokemon in dark places like caves and forests!
-> Name the imte again | Dusk Balls will help to catch Pokémon... etc.Girl @ Poké Center: Maybe you could search for my Poké Ball.
-> Do you perhaps want to search the Poké Ball for me?Girl (after selecting "no"): Ok Ill have to ask another Trainer...
-> Okay, I'll ask another trainer, then...Girl (delivering the item): Oh. What`s that? Is that my Poké Ball?
-> Oh, what's that? | wrong apostrophe ^^Old man @ Pokécenter (after quest): Rare Pokémon are mostly stronger than common ones.
-> Rare Pokémon often seem stronger than common ones. I don't really know why that is... | His reason (not quoted here) is circular as well.Ranger (before trading): Oh, excellent! Lets trade!
-> Let's trade!Rodney (before the battle): Oh! [player]!...You won your second Badge already!?
-> You've wonRodney (about Thundrome Pass): Its known for having lots of thunderstorms and rain here. It has something to do with some temple or something...
-> It's known for the heavy thunderstorms that pass by occasionally. I thought it had something to do with a temple...Rodney: Can we battle? Pretty please?
-> Can we battle? Please? | I don't know what that "pretty" does here.Rodney (after the battle): I enjoyed it
-> This line again... Is it used wrongly for Keira's first battle, then?Rodney (after battle): I'm gonna go train before my Gym battle.
-> I'm going to train before taking on the Gym Leader.---Blackleaf Woods---
Punk Guy Gregory (after battle): Over there is the exit but, if you walk on, you may not be able to find the way back!
-> Over there is the exit, but if you keep on walking, you may not be able to find your way back!---Crestlight Gym---
Gymdude: Hello, there! You found Damon in Blackleaf Woods?
-> You've found Damon in Blackleaf Woods?Gymdude: Well, then, the Leader of this Gym specializes in Dark-type Pokémon. Maybe this will help you: (fresh water)
-> No tip at all? Maybe add something like: "Well then, Damon is specialized in Dark-type Pokémon. You have to know that Psychic-type attacks do absolutely no damage against them! I think it's best if you bring a Bug or Fairy-type Pokémon with you. Either way, this item will help you in any case:"
Also, since it's the second Gym, you may add that you can select three Pokémon again, as reminder. Damon (before battle): You made it here... Good. You have passed my test in Blackleaf Woods.
-> You've made it here... good. You've already passed my test in Blackleaf Woods, so I knew you would show up soon.Damon: Many people fear Dark-types, this is because they do not understand them, they can be magnificent!
-> Many people fear Dark Pokémon, but his is merely because they don't understand them. They, too, can be trusty partners. Furthermore, they are magnificent in battles!Damon (after battle): As your reward, you have earned this Darkness Badge.
-> As a reward for your efforts, you have earned the Darkness Badge.Damon (after battle): I wish you many victories along your journey, [player]!
-> I wish you many victories on your journey, [trainer]!Gymdude (after battle): What an amazing battle! You are the new master of the darkness!
-> What an amazing battle! You were certainly able to master the darkness!I hope it is appreciated! I will continue with Route 3 and onwards.
One last note though, where can I post bugs or other thoughts that have no relation to the text?
I've tried to leave out corrections that are based (too much) on personal preference, but in some cases I just suggest an altered sentence. I don't try to be mean, I just want to show my love for the game by making it a bit better on a textual level, as far as I can do anything about it as non-native speaker. 
