Set extensions.torbutton.prompted_language pref
Set extensions.torbutton.prompted_language pref

In order to avoid language selection prompt. Before #18019 it was only
shown when opening a new tab. Now it is shown when loading a page.

boklm/tbb-testsuite,boklm/tbb-testsuite,boklm/tbb-testsuite,boklm/tbb-testsuite,boklm/tbb-testsuite