I can reproduce the same issue as you when I try to speak non-English. Except my GBoard does not crash and just tries to open Speech Services from Google.
I believe your GBoard is crashing because it is expecting Google Speech Services to be installed on your device and I presume you never installed.
Installing it on your device will stop the crash but rather than giving the network permission to GBoard you'd need to give it to Google Speech Services instead.
Because Google Speech Services doesn't seem to work at all with the network permission denied, not for English and not for other languages with the language packs downloaded.