gtk-theme-switch2: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/gtk-theme-switch2 - from package: gtk-theme-switch

You may install the required package with command apt-get install {package}

Error in other languages:
gtk-theme-switch2: bevel nie gevind nie
gtk-theme-switch2: comandă negăsită
gtk-theme-switch2: comando não encontrado
gtk-theme-switch2: commande introuvable
gtk-theme-switch2: command not found
gtk-theme-switch2: käsku ei ole
gtk-theme-switch2: không tìm thấy lệnh
gtk-theme-switch2: komanda nerasta
gtk-theme-switch2: Kommando nicht gefunden.
gtk-theme-switch2: kommandot finns inte
gtk-theme-switch2: komut yok
gtk-theme-switch2: nie znaleziono polecenia
gtk-theme-switch2: níor aimsíodh an t-ordú
gtk-theme-switch2: no se encontró la orden
gtk-theme-switch2: no s'ha trobat l'ordre
gtk-theme-switch2: opdracht niet gevonden
gtk-theme-switch2: parancs nem található
gtk-theme-switch2: perintah tidak ditemukan
gtk-theme-switch2: príkaz nenájdený
gtk-theme-switch2: příkaz nenalezen
gtk-theme-switch2: команда не найдена
gtk-theme-switch2: командата не е открита
gtk-theme-switch2: 命令找不到
gtk-theme-switch2: コマンドが見つかりません