Hello!
To change languages, it's under Menu > Settings > Language Support.
To remove Mumble, it can be done in Install/Remove Software (Synaptic Package Manager) or, in a terminal window [CTRL-ALT-T], type the following...
sudo apt-get remove mumble
Sometimes, a logout/logon or reboot may be required for menu entries to disappear. If they're still around after THAT, the .desktop files that comprise the menus are located in two places:
/usr/share/applications
/home/<USERNAME>/.local/share/applications
To see files or folders beginning with '.', 'Show Hidden Files' must be checked (enabled) in the file manager. To delete anything outside your home directory, you have to logged in as root...
73 DE N4RPS
Rob