Hello,
There is a problem that we will try to solve together with WPML support.
As a workaround for you, next steps:
1/ Add https://prnt.sc/zvatyTCmRfzw
2/ Add item in mobile menu https://prnt.sc/Urt-UOzchhk0
3/ Then go to menu translation https://prnt.sc/d_b2rpVnG459
4/ Add a similar item but another language – https://prnt.sc/YU7_Jwkq_xEJ
5/ Check the result on the frontend.
Regards