Holla!

This is a collection of all possible Trades and Gifts of in-game NPC's credentials in every language possible.
All Generation I-IV Trades are obtained at the lowest level possible with thorough research.
Please refer to the Guide.txt included in the collection archive for details on what to edit to make any of them to your personal liking.
 
NOTE: If you're reading this in the future and a new game came out, please do not expect any updates with its trades immediately or anytime soon, unless users contribute them to me.
 
Credits:
@Taargüs Taargüs - For providing the PK5s for all languages of B2W2 Yancy and Curtis trades, and also the Korean B2 Petilil!
@RobustRabbit - For providing CHT SM and USUM trades!
@ViolentDarkBrown - For providing all languages of trades in Let's Go, Pikachu/Eevee, Sword/Shield, Brilliant Diamond/Shining Pearl, and Scarlet/Violet!
Serebii and Bulbapedia - For providing the location whereabouts and details for the lowest levels possible of NPC's requested Pokemon. (Even though they contradict each other sometimes...)
And of course, anyone who reports errors!
If you would like to share this collection archive around other websites, you are free to do so, but please give credit to the mentioned users for their generosity to contributing. Thanks!
 
PSA: If PKHeX flags any Pokemon as invalid, please do collate the files that do so and report them in the PKHeX forum. And if you think a Gen 1-4 Pokemon can't be at a certain level, please do notify me about it (and provide sources).
 
 

Saves for the first Pokémon Stadium released in 1998 only in Japan, Stadium 2 (Stadium 1 in the west), and Pokémon Stadium Gold & Silver (Stadium 2 in the west).
Stadium (1998):
Dodrio GB speed unlocked. Stadium 2:
R-2 complete. Hyper COM level unlocked in Kids Club. All 151 Pokémon registered in Hall of Fame. Psyduck ready to be claimed by accessing it. Gorgeous Box Kabuto transferable at Oak's Lab. NOTE: My in-game trade/gift collection has every file for the random gifts from clearing the Gym Leader Castle on both rounds that you can just modify to your liking such as randomizing IVs or making them Shiny. Gold & Silver:
R-2 complete. Very Hard COM level unlocked in Mini-Games. Pokémon Academy complete. Special Farfetch'd and Gligar both ready to transfer. NOTE: I just included an international save for this one because they're interchangeable.

These are the saves from the famous Twitch phenomenon livestream that began with Pokemon Red on February 12, 2014 at 23:16:01 UTC. 
It contains the non-ROM hack save files for the main series playthroughs of the following games:
Pokemon Red
Pokemon Crystal
Pokemon Colosseum
Pokemon Emerald
Pokemon XD: Gale of Darkness
Pokemon Platinum
Pokemon Black
Pokemon Sun
Full credit to /r/twitchplayspokemon for the saves.