It doesn't work. The output is:
kbuildsycoca4 running...
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Keywords in "k3bsetup.desktop" is not compliant with XDG standard (missing trailing semicolon).
"KConfigIni: In file /usr/share/kde4/services/muon-knsplasmoids-backend.desktop, line 113: " Invalid entry (missing '=')
"KConfigIni: In file /usr/share/kde4/services/muon-knsplasmoids-backend.desktop, line 114: " Invalid entry (empty key)
"KConfigIni: In file /usr/share/kde4/services/muon-knsplasmoids-backend.desktop, line 115: " Invalid entry (missing '=')
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Categories in "/usr/share/applications/gnome-power-panel.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Categories in "/usr/share/applications/im-switch.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Actions in "/usr/lib/libreoffice/share/xdg/calc.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Categories in "/usr/share/applications/gnome-region-panel.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Actions in "/usr/lib/libreoffice/share/xdg/impress.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Categories in "/usr/share/applications/gnome-background-panel.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Categories in "/usr/share/applications/gnome-color-panel.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Categories in "/usr/share/applications/gnome-screen-panel.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Categories in "/usr/share/applications/gnome-user-accounts-panel.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Actions in "/usr/lib/libreoffice/share/xdg/draw.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Keywords in "/usr/share/applications/firefox.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Actions in "/usr/lib/libreoffice/share/xdg/math.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Categories in "/usr/share/applications/pycode-browser-book.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Categories in "/usr/share/applications/pycode-browser.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry MimeType in "/usr/share/applications/pymol.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Categories in "/usr/share/applications/unity-region-panel.desktop" is not compliant with XDG standard (missing trailing semicolon).
kbuildsycoca4(4380) KConfigGroup::readXdgListEntry: List entry Actions in "/usr/lib/libreoffice/share/xdg/writer.desktop" is not compliant with XDG standard (missing trailing semicolon).

In this case then, as it is a Kubuntu specific addon you need to file a bug with Kubuntu or ask them which packages your system may be missing - it is possible the functionality has been removed or otherwise integrated elsewhere.

So it means that I should ask in Kubuntu forum, not KDE forum?

Yes - that would be a good step to take, as the folks there should be more familiar with this custom module.
Sorry that we can't help further.

thanks for your help

this link will help you https://www.kubuntuforums.net/showthread.php?65007-No-Language-input&p=347782#post347782

Hi, I'm on Mint 16 KDE now and still don't see the Language Input tab. I think that this is an KDE's issue, not distro's. And it says "E: Unable to locate package language-selector-kde" when installing language-selector-kde.

As previously stated, this module isn't shipped as part of KDE - the Kubuntu forums are the best place to receive support for this issue.
If they cannot diagnose the cause of the issue, I would suggest filing a bug report on Launchpad against the appropriate component.

No, I don't use Kubuntu right now but Mint and this issue still exists.

I've spoken with the packagers of this. Turns out the module was originally shipped as part of Kubuntu, but was later withdrawn as it was unmaintained.
ie. This functionality no longer exists.

What are you attempting to achieve?

I want to install my language input, Vietnamese. I use Dvorak keyboard.

I would suggest searching in your package manager for l10n/i18n packages ending with -vi, which should supply Vietnamese translations.

The l10n-vi have been already installed. I can't find the i18n with -vi. What do they do?

The packages are named either l10n or i18n. In this case, you have it installed, so everything should be sorted.
These packages contain the translation files needed to allow an application to display a translated language.

Still missing Language Option