Dialog warning about readonly symbol library broken

Description

If you try to safe a symbol to a readonly library, you get the following dialog box:

Some text seems to be missing here

Steps to reproduce

For example follow the steps from #7352 (closed) while skipping step 4.

KiCad Version

Application: Eeschema

Version: 5.99.0-unknown-r25448-fabafe71, debug build

Libraries:
	wxWidgets 3.0.5
	libcurl/7.71.1 OpenSSL/1.1.1i-fips zlib/1.2.11 brotli/1.0.9 libidn2/2.3.0 libpsl/0.21.1 (+libidn2/2.3.0) libssh/0.9.5/openssl/zlib nghttp2/1.41.0

Platform: Linux 5.10.10-200.fc33.x86_64 x86_64, 64 bit, Little endian, wxGTK, gnome-xorg, x11

Build Info:
	Date: Jan 30 2021 18:43:07
	wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.73.0
	OCC: 7.5.0
	Curl: 7.71.1
	ngspice: 33
	Compiler: GCC 10.2.1 with C++ ABI 1014

Build settings:
	KICAD_SCRIPTING=ON
	KICAD_SCRIPTING_MODULES=ON
	KICAD_SCRIPTING_PYTHON3=ON
	KICAD_SCRIPTING_WXPYTHON=ON
	KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
	KICAD_SCRIPTING_ACTION_MENU=ON
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON
	KICAD_STDLIB_DEBUG=OFF
	KICAD_STDLIB_LIGHT_DEBUG=OFF
	KICAD_SANITIZE=OFF