So after some testing, I can now confirm that the problem lines not with the actual, physical BT keyboard, but with the virtual, on-screen keyboard you're using. I had drifted away from Swiftkey because a particular bug (selecting multiple words using shift+directional keys in BT keyboard, if you were wondering) and started using Google's GBoard. I've tried a third keyboard, the Xperia Keyboard that comes preloaded with my Z4 tablet; and I can confirm: it's not the BT input, it's how the software keyboard interprets stuff. I've lost Swiftkey's word prediction at the bottom of the screen and I've lost GBoard's left-Alt (not to be confused with the Alt-right, drum roll) special character pop-up, but I've regained accented characters across my apps. Hope this helps!!
I'm having a problem that is only happening on your app. I'm using a Z4 Xperia tablet with the default BKB50 bluetooth keyboard that comes with it. I'm using the default software and default ROM (no editions of any kind). Sometimes, the input behaves wierdly; here's 2 cases in particular. 1. I start typing and some keys are interpreted repeatedly: "IIIIII sstaaaaaarrrrrttt tyyyypppppinggggga aaandddddd soooommmmmeeee" etc. 2. If I type the accent key, all letters will continue appear with accents until I either type a space (space bar) or a period (.) ejemplo de casos donde los áćéńtos no dejan de aparecer. sóĺó´dejan de aparecer cuando escribes (espacio) o (punto). these two cases happen only on your app. let me know if I can send a file, a log or something that can help you find and fix the problem. keep up the great work!!!