common: Disable language chooser confirm button until a language is selected

Make the button insenstive until a language is chosen as per:
https://wiki.gnome.org/Design/SystemSettings/RegionAndLanguage
11 jobs for <span class="ref-name">common-language-chooser-button-insensitive</span> in 24 minutes and 41 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #91823
build

00:02:23

 
  Test
passed #91826
armv8

00:13:46

passed #91825
asan

00:02:07

failed #91827
allowed to fail
ppc64le

00:12:59

passed #91824
test

00:00:52

 
  Manual
manual #91828
allowed to fail manual
flatpak
manual #91831
allowed to fail manual
msan
manual #91829
allowed to fail manual
tsan
manual #91830
allowed to fail manual
ubsan
 
  Review
manual #91832
allowed to fail manual
review
manual #91833
allowed to fail manual
stop_review
 
Name Stage Failure
failed
ppc64le Test
Full log written to /cwd/_build/meson-logs/testlog.txt
FAILED: meson-test
/usr/bin/python3 -u /usr/bin/meson test --no-rebuild --print-errorlogs
ninja: build stopped: subcommand failed.
Uploading artifacts...
./*.log: found 1 matching files
_build/meson-logs/: found 4 matching files
Uploading artifacts to coordinator... ok id=91827 responseStatus=201 Created token=e-TSB8NJ
ERROR: Job failed: exit code 1