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