There is a problem while loading data files/sources when using a Turkish OS.

Is this modified data from what we distribute? The log is showing many "i" characters as not the base US language "i" or "I", and many of the items will be dependent on those being exactly consistent throughout the data (or things will be viewed as missing)

It's a translation issue with the Turkish language on his Operating System. I tried to help and it's actually altering the words in the data and gamemode. Makes PCGen unusable in Turkish.

Most likely we’re not explicitly setting the locale we need to when loading lst files or the like. We extensively use toUpperCase() which would utterly break with the turkish i. I’ve done some basic fixes but don’t have an easy way to test this.

Can you try with the PR in https://github.com/PCGen/pcgen/pull/4765 applied? It is a mechanical change but may actually help.