The Caliphs conquered non-muslim lands who didn't speak arabic and I assume there must have been conversions during this time as well. So, did the friday khutbah take place in arabic there or was it in the local language?
For example: Umar RA conquest of Persia here
Caliph Umar ordered a full invasion of the Sasanian empire in 642, which led to the complete conquest of the Sasanians around 651.
According to here , Arabic was not a language in this empire