I'm decorating a two layer butter cake and I was thinking of adding a layer of sliced fresh strawberries in between the two layers together with some strawberry flavored Bavarian cream. I will be serving the cake in two days. Will the strawberries give out too much liquid and make the cake soggy?
Generally, no they should be fine. You'd have more of an issue with frozen than fresh. It would take fresh strawberries a long time to release enough moisture to cause any significant amount of sogginess.
The issue you're more likely to run into depending on the size of your strawberries, the density of your Bavarian cream, levelness of your cake, and the weight of your top layer is that they can act like rollers and friction between the two layers will be low. If the cake is tilted wrong, the top layer will just slide right off. I've definitely had it happen - ruined a cake for a charity event :(. Make sure the strawberries are cut into bits - not halves or slices and preferably fold them into the cream to prevent this from happening. All the flavors will still be there, but your cake will be safer.
I also think that the strawberries won't be much of a problem. But if you use lots of them, or if they are frozen, or if you want to use other, moister, fruit in the future, you could run into problems. And you would be relieved that there is a solution.
The solution against cake getting soggy from fruit is to simply seal the cake layers against moisture. The traditional way is to glaze with apricot jam - you brush a very thin layer of melted apricot jam on the cake layer, and put the fruit on it after it has cooled. The amount is so small that the taste is not noticeable, and it is also practically invisible. Alternatively, you can use other glazes, such as slightly thickened simple syrup (cooled, so it won't seep into the layer itself), starch cooked in water (evtl. with some sugar), other jams, or commercially available sealers (Dr Oetker sells them in sachets).