General note:

2 weeks ago, the game worked with proton 6.3.8 - so repeat the following steps for other proton versions, if necessary.

After installing winetricks & protontricks, use this command:

WINEARCH=win64 WINEPREFIX=${HOME}/.steam/steam/steamapps/compatdata/105450/pfx/ winetricks d3dx9 mfc42 winxp l3codecx corefonts

Explanation of the winetricks:

audio issues? -> l3codecx*

can't enter aoe3 key due to font issues? -> corefonts

key registration issues? -> mfc42

Additional issues:

• "fonts2.xml not found" -> go to your AOE3 steam dir and change the UTF-value in the "fonts2.xml" from "16" to "8" in the first line. if that still doesn't do the trick, copy the fonts files into your wine dir, as discussed here (https://askubuntu.com/questions/86335/installing-other-fonts-on-wine)
  
  

• if the error persists(*), manually copy the l3codecx into your wine folder. detailed instructions can be found here under paragraph "Acquiring the l3codecx.ax file" (https://appdb.winehq.org/objectManager.php?sClass=version&iId=3795)