you can complete the game in english first, if you want to experience the story. (and dont speak/understand the welsh language).
when you finish the game in english it returns you to the main menu, go to option change your language in audio to welsh. go back to the main menu and press the very top option (Continue in english). you will start back right before the Bells & Axe mission and finish the game from there (about 10mins).
1: Beat Game in English, Game returns you to main menu after credits. (note: continue button at the top of the main menu)
2: Got to Options in main menu, then audio and change it from english to welsh.
3: impossible to understand if you do not know welsh (maybe memorize the main menu beforehand) press O to go back to the main menu.
4: Press the top Button ( Continue Button noted earlier in english)
5: Game will restart you right before getting on the train to the Bells & Axe Mission.
6: Finish the game ( you should have already finished in english and know how to progress).
7: Trophy unlocks at end game cinematic for the normal ending.
Note: Final Mission with countdown may be skippable thru the alternate ending and still unlock the trophy. personally unlocked thru normal ending.