Thanks Jannas for your query !
The snapshot above is an advance setting part of SOI task on console. This dropdown contain static list of regional languages that Microsoft usually supports. Here user has to select the appropriate language (default is English (US) ) and that regional lang should supported by OS package that he has imported.
My prediction of this case is the OS package the user is using supports the English(US) as regional lang and hence it is working fine with this lang. But this package does not support English (UK) as regional lang and hence user is getting this pop up during SOI in automation.
Hope this helps!!