The question is interesting, but clearly under closure. I was also interested in the question of multi-platform development, so I will try to briefly outline my thoughts on this.
Option A. Productivity is not needed, more important is the speed of development.
There is definitely something from the interpreted languages - Java, Python, something else. Not my option, so there is little I can say.
Option B. Performance is important.
There is one option - C / C ++, but the problem of multiplatform graphics comes up. Two options look more or less real:
Qt is a huge library, well documented, with a large community, in general, an option is good for everyone - BUT! All this comes with completely cannibal licensing terms. This option is suitable either for open source crafts or for large high-yield projects with a serious development budget. If your project is somewhere in the middle, all profits will go to Qt owners.
WxWidgets is the opposite. No problems with the license, but the full range of open source charms - scanty and mostly outdated documentation (the notorious “The Book” by WxWidgets), the complete lack of support, etc. etc.
In general, the choice is small and difficult.