Comment 52 for bug 481656

I 've spent a good few additional hours editing OSM data with the Java-based JOSM application, and since I started running the application by setting "XMODIFIERS=" for iBus I have no longer experienced any problem with text entry: neither failure to get any input text, nor the inability to enter special characters for Spanish.

So that _may_ look like a valid workaround, however, it's just based on my own experience for a limited time, and your mileage may vary.