Here is the full list of all 50 Lethis - there are Path of Progress achievements.
You built over 10.000 box tiles of road, all cities together.
You completed Chapter IX
Your unemployment rate went over 50 % (with a population over 2000 inhabitants).
You completed part one (Chapters I to V)
You’ve finished building the Observatory during summer.
You’ve built 50 road blocks during one game.
You’ve built 5.000 buildings, all cities together (excluding roads, bridges and roadblocks).
You managed cities for ten hours.
You completed a mission without cutting down trees or bushes (outside tutorial missions).
You captured 20.000 faes in one game.
You have 7 functioning mines in one city.
You destroyed 1.000 buildings, all cities together.
You completed the tutorial missions.
100 houses withered by time, all cities together.
You’ve built 50 Automaton factories, all cities together.
You've exported a total of 100.000 units of silk, all cities together.
You’ve listened to 100 pedestrians, in all your cities together.
You responded to 20 of the Emperor’s requests, all cities together.
You've exported 100.000 units of alcohol (Absinthe or beer), all cities together.
500 houses have been exorcised, all cities together.
A pirated copy of the game has been detected. But you bought the game, so you’re forgiven.
You entered a second valid cheatcode in the console.
You responded to 3 scientific requests during Chapter 24.
Enter « Ambrosia » in the cheat console.
80.000 potatoes harvested in one harvest, congratulations !
You completed the campaign on maximum difficulty.
You Completed the campaign on “normal” difficulty or harder.
You completed the campaign on “easy” difficulty or harder.
You completed part two (Chapters VI to X)
You completed part 3 (Chapters XI to XV)
You completed part four (Chapters XVI to XX)
You completed part five (Chapters XXI to XXV)
You completed the epilogue (Chapter XXVI)
You managed cities for fifty hours.
You built a monument, only to destroy it right away (And boy, did it hurt !)
Finish a game while having experienced three revolts.
You produced 20.000 units of fish and 20.000 units of potato during one game.
You built the four monuments during a sandbox game.
You’ve finished building the Botanical Garden during winter.
You’ve finished building the World Exposition during spring.
You’ve finished building the Zeppelin Hangar during autumn.
You’ve experienced a revolt during the month of Germinal.
You took a screencap of the city you’re the most proud of.
You built each type of farm during one game.
You’ve built 25 steam-powered buildings during one game.
You cut down 50 trees during a game.
You’ve witnessed your very first revolt.
Unlock the Winter garden, Summer sky, Springtime science and Autumn flight achievements.
You didn’t respond to 20 of the Emperor’s requests, all cities together.
You took time to watch the credits.