99.99% it will be English thread - it is the defacto standard for non press fit BB, all American and Asian bikes and even most newer Italian bikes are English thread- you can check the specs online but if your BB shell width is 68 or 73mm then it will be english (Italian has a 70mm BB shell on the bike). Also for English thread BB's the Drive side cups have a reverse (left hand thread) that means both DS and non DS tighten towards the rear. The thread size is different between italian and english also. Are you sure that your existing chain ring will fit the BCD of 105 crank and give you the correct chainline?
Has nothing to do with the number of teeth Shimano 105/Ultegra 10 speed BCD is 130mm for a double. so for a 5 bolt chain ring it should measure 76.4mm from the centre to centre of each mounting bolt / hole. You can measure it up. Probably better to buy a complete crank and just remove the 39T chainring - will look better too.