I tried to localize Netrunner the Serbian language. Localization does not work correctly, some KDE programs refuse to work (eg. ktorrent), Gnome programs are not localized, time and date can not be localized. I came back to US manually change the file /etc/default/locale

You need to install the serbian language pack I guess for all the applications to change their language. Also notice for a full language switch you need to reboot the system.
The language packs can be found with muon or synaptic.

For time and date right click on the clock widget in the panel. There you can setup different timezones if you wish. The format of the time and date is changed after a reboot.

Thank you to all know that I’m doing, but unfortunately localization not working properly.
I tried and #dpkg-reconfigure locale but it does not work as well in other KDE distributions

Did you install the language packs for your language ?
You need the language-support-[2-sign-language-code] package aswell as the kde-l10n-[2-sign-language-code] package installed.

Yes I install it kde-l10n-sr, also instal language pack for Firefox, Thunderbird, Libre Office…
I setup the control center the country of Serbia, setup Serbian language do restart.
Localization does not work correctly.

What applications do not work ? Perhaps its simply because there is no translation available in your language.

Something does not work as it should, something is wrong when sudo dpkg-reconfigure locales. I do not get the second part where I choose default language.

sudo dpkg-reconfigure locales Generating locales... de_AT.UTF-8... up-to-date de_BE.UTF-8... up-to-date de_CH.UTF-8... up-to-date de_DE.UTF-8... up-to-date de_LI.UTF-8... up-to-date de_LU.UTF-8... up-to-date en_AG.UTF-8... up-to-date en_AU.UTF-8... up-to-date en_BW.UTF-8... up-to-date en_CA.UTF-8... up-to-date en_DK.UTF-8... up-to-date en_GB.UTF-8... up-to-date en_HK.UTF-8... up-to-date en_IE.UTF-8... up-to-date en_IN.UTF-8... up-to-date en_NG.UTF-8... up-to-date en_NZ.UTF-8... up-to-date en_PH.UTF-8... up-to-date en_SG.UTF-8... up-to-date en_US.UTF-8... up-to-date en_ZA.UTF-8... up-to-date en_ZM.UTF-8... up-to-date en_ZW.UTF-8... up-to-date sr_ME.UTF-8... up-to-date sr_RS.UTF-8@latin... up-to-date sr_RS.UTF-8... up-to-date Generation complete.
ег. ktorrent program does not work, in another KDE distro localized ktorrent works
synaptic, dolphin etc… not localized
I solved the problem by manually editing files, ktorrent installed manually, I create manually .bash_profile.