Error not displayed after QR code scanning failure: "TypeError: 'dict' object is not callable" for "_"

Jun 19 12:36:11 amnesia tca[8488]: ERROR:TCAApplication:response-error from portal : Command failed with returncode 1
Jun 19 12:36:11 amnesia tca[8488]: Traceback (most recent call last):
Jun 19 12:36:11 amnesia tca[8488]:   File "/usr/lib/python3/dist-packages/tca/ui/main_window.py", line 384, in on_qrcode_scanned
Jun 19 12:36:11 amnesia tca[8488]:     set_error(_(
Jun 19 12:36:11 amnesia tca[8488]:               ^^
Jun 19 12:36:11 amnesia tca[8488]: TypeError: 'dict' object is not callable

I believe this is a regression introduced in 5.14 by 31e4b9df. One instance of the bug was fixed in 30b6842e, but some others remain, or could start happening whenever we start using localized strings in the affected code paths.