Onlyoffice 8.3.0.97 (flatpak) spellcheck reverting to default keyboard language settings

[Skinoku]

In every app of version 8.3.0.97 (flatpak) every time I press a key on the keyboard, no matter what language is set as default for spellcheck, it reverts back to the one used as default of the system keyboard.
This is really annoying because I have for example a Linux machine with US keyboard (international) and if I want to write in other languages I can't because it goes back to English.
I cannot switch the system keyboard to another language because of course I will not be able to input certain symbols.
The expected behavior is that the spellchecker follows default language settings and IGNORES the system-wide keyboard language settings.