As has been mentioned previously in this thread, somebody whose native language is not English and who is experiencing these problems (and who is good with Linux configuration) needs to step up and help us with this.
All the main OSMC devs are English speaking only and only have access to UK and US keyboards to test with.
As such we not only don’t have access to the hardware necessary to test the problem (Keyboards with non US / UK layouts) we also don’t have the experience of being a multilingual computer user and dealing with the issues that surround this such as configuring keyboard layouts, non English fonts/character sets etc, and without specific knowledge of another language, its keyboard layout and how it is supposed to work, it’s next to impossible for us to make any further progress on this, especially with so much other work competing for precious development time.
So until someone with the right combination of skills and knowledge steps forward to help with this, this problem is likely to remain unsolved.