This bug was filed from the crash reporting server and is br-d0662f7e-8e98-491d-9834-761b6550b6d5.
Tools>Options>Language settings>Languages>check/uncheck DecimalSeparatorKey then click OK causes the crash.
I can't confirm it with
Version: 184.108.40.206.alpha0+ (x64)
Build ID: 01837a85004a6f891a09c0a63ed7eff75d634827
CPU threads: 4; OS: Windows 10.0; UI render: GL; VCL: win;
TinderBox: Win-x86_64@62-TDF, Branch:master, Time: 2019-09-01_00:07:05
Locale: en-GB (de_DE); UI-Language: en-US
On Win10 with LO 220.127.116.11, I don't reproduce this.
Could you give a try to 6.3.1? Indeed, perhaps you just encountered a bug already fixed.
Right. I did not realize my work computer was out of date. With
Version: 18.104.22.168 (x64)
Build ID: e979878b49a48dab15ebe528f238b88125e32c65
the bug has vanished.