Here is the full list of all 15 If Found... achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
Play the game in Irish.
After finishing the first chapter, go to the last chapter.
Choose the Mayo flag in the character creator.
Erase for the length of one Mass.
(That we may live to see this time next year.) Write every diary entry in Opening.
Finish ‘Opening’ chapter.
Draw for the first time.
Choose the transgender pride flag.
Finish ‘The Anomaly’ chapter.
Finish ‘The Back of Beyond’ chapter.
Finish ‘Cassiopeia was over Keel’ chapter.
Finish ‘Coming and Going’ chapter.
(Do you understand?) Read an Irish annotation.
Find Colum drinking coffee.
Erase for the first time.