Hello fellow buccaneers, welcome to my guide.
I didn't find any, so i decided to write one.
I hope to help you with my experience in the achievements of this game and with the knowledge i gathered around the web.
I beg your pardon in advancement, for this is not my first language, and for my lack of experience in creating guides, so no fancy images and pretty phrases, just descriptions straight to the point.

Maneuver Master
Fire 50 single salvos from both the starboard-side and the port-side cannons.
With the autofire disabled from the settings, you need to position your ship between 2 enemy ships, then press the fire button to shoot from both your sides at the same time. (if you want to farm this, just use rusty bar shots, both to immobilize and to not sink the ships).

Treasure hunter
Complete all 21 legends.
Self-explanatory, here is a link to a very good guide:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=1212953324

Best Actor
Get an Oscar in 3 categories. (3 Oscars in the hold).
In the mission "Time Loop" taken from the Seekers faction, near the end, you'll gain one of these objects, repeat the same mission 3 times keeping these particular objects in the hold to gain this achievement.

My Domains
Destroy 10 forts
Self-explanatory.

The Merchant
Sell 1,000,000 piastres` worth of valuables.
Self-explanatory, you'll probably gain this simply playing. But if you want to farm this, i advise to find 2 cities near one another, one with the sale (green badge) and with goods like silverware or silk, and one with the overprice (red badge); just purchase from the "green" city and sell in the "red" city, travelling back and forth.

True Pirate
Reach the maximum faction rating with the pirates.
Self-explanatory, just take only their missions and fight every quest battle or random encounter with their flag raised.

Sharp as a Razor
Finish 25 enemies with a ram attack.
Self-explanatory, take the hull life bar (the lowest one) to a sliver, and then RAM' EM.

The Hunter
Win 10 boardings without taking any losses.
Self-explanatory, destroy their sails, shred the enemy ship crew with shrapnel or poisonus cannonballs, board the enemy ship and mop up the survivors.

Sea of Poison
Earn the Poisonous Asp reputation.
Put on you farming pants, get you grinding gears, and start shooting poisonus cannonballs. For example, go in the Ghostly Sea (the northern map) and go back and forth the 2 Seekers most north-eastern settlements, fighting returners using as much as possible poisonus cannonballs (you can purchase them in the northern settlement).
You can check the progress to this title in the capitain's log, 4th section, second page "Reputation", snake badge.

All on Board
Assemble a full 15-man crew.
During gameplay, you'll come across several "officers" you can recruit in you crew, here is a link to a very good guide:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=1212953324

Fearless
Get sunk by the sea monster Leviathan 3 times.
Take your weakest ship, strip it from every enhancement (not sure if it is necessary, but you can't never be sure), and just sail over the border of the map to get attacked and sunk by the sea monster Leviathan.

Train Hard, Fight Easy
Complete the tutorial.
Complete all the "Pirate Academy" missions.

Tempest
Witness 2 concurrent tornados.
Self-explanatory, it's a random encounter during any sea battle.

Conqueror of the Lands
Complete all Secret Land quests.
(DLC content) landing by the palm tree bronze badges, there are 6 or 7 different casual quests you need to complete for this achievement.

Emperor's Friend
Complete the Emperor's Daughter legend.
(DLC content) finish the relative legend.

Kind Doctor
Heal Basil
(DLC content) during your pirate city mission "Wedding Woes", instead of boarding and capture the ship sink it, BUT you need the "Fist aid" captain skill at the max to gain this achievement.

Animal Advocate
Let Krakens go without a fight.
(DLC content) during your pirate city mission "Animal Planet" (not sure if other kraken missions count toward this achievement), sail to battle the kraken but do not fire a single shot during the entire encounter, both against the children and the mother; after some time they will go away and with the reward for the mission you'll get this achievement.

Fraud
Return the forged painting.
(DLC content) during your pirate city mission "Art of Thievery", instead of complete the mission in the way intended, sail to one of the Order cities in the Eastern Sea, pay for a forged painting and give it to complete the mission and get this achievement.

Righteous One
Kill the spawn of hell.
(DLC content) during your pirate city mission "Buying bodies, Cheap", return with 10 wounded men (just go to battles with a healing stone and never cure you wounded men, krakens and Returners can do fine) and choose the "shoot" option, BUT you need the "Shooter" captain skill at the max to gain this achievement.

Maestro
Keep the violin.
(DLC content) during your pirate city mission "Remarkable Violin", after finding the quest object, upon returning choose the "keep it" option, BUT you need the "Mystic" captain skill at the max to gain this achievement.

Cunning Bastard
Cheat in the battle for the title.
(DLC content) during your pirate city mission "Champion's Belt", choose one of the option to cheat the fight (i'm not sure if something is necessary to able you choosing one option or another, i can say i had very bad relations with the pirate faction).

Sun Wukong's spirit.
Place Sun Wukong's Statue and Sun Wukong's Golden Staff at simultaneously.
Very misleading description, in the equipment section you simply need to put on the Sun Wukong's Statue and the Golden Cudgel at the same time (you can get them in some shops, but they can easily be found around, so just be patient).

I currently don't have this achievements, due to the lack of online opponents, or because i'm doing something wrong, in any case feel free to add me and try to get these toghether.
edit: i tried fighting someone, but my ship keeps teleporting some distance on the left side, giving me no choice to effectively fight, someone knows if it's a bug or due to poor connection?

Sea Wolf
Win 25 games online.
Self-explanatory

The One
Face a developer online, or against 10 players who have this achievement.
Self-explanatory

That's it guys, if you have anythig to say or change, please feel free to comment and suggest.