When I place the J1a Texas and start the engine it haets up until 21,5 °C, then the game crashes and I can't join the world anymore

I guess your missing some sounds. Check again if the sounds are in the resource pack. There should be a folder called "sounds" with the taxas folder and sounds inside

There is no sounds Folder :/

then remove the sounds from the locomotive json in rolling_stock/locomotives/texas. You can open the file with any text editing program (Notepad++ or the default notepad)