eiskaltdcpp-gtk3: 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/eiskaltdcpp-gtk3 - from package: eiskaltdcpp-gtk3

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

Error in other languages:
eiskaltdcpp-gtk3: bevel nie gevind nie
eiskaltdcpp-gtk3: comandă negăsită
eiskaltdcpp-gtk3: comando não encontrado
eiskaltdcpp-gtk3: commande introuvable
eiskaltdcpp-gtk3: command not found
eiskaltdcpp-gtk3: käsku ei ole
eiskaltdcpp-gtk3: không tìm thấy lệnh
eiskaltdcpp-gtk3: komanda nerasta
eiskaltdcpp-gtk3: Kommando nicht gefunden.
eiskaltdcpp-gtk3: kommandot finns inte
eiskaltdcpp-gtk3: komut yok
eiskaltdcpp-gtk3: nie znaleziono polecenia
eiskaltdcpp-gtk3: níor aimsíodh an t-ordú
eiskaltdcpp-gtk3: no se encontró la orden
eiskaltdcpp-gtk3: no s'ha trobat l'ordre
eiskaltdcpp-gtk3: opdracht niet gevonden
eiskaltdcpp-gtk3: parancs nem található
eiskaltdcpp-gtk3: perintah tidak ditemukan
eiskaltdcpp-gtk3: príkaz nenájdený
eiskaltdcpp-gtk3: příkaz nenalezen
eiskaltdcpp-gtk3: команда не найдена
eiskaltdcpp-gtk3: командата не е открита
eiskaltdcpp-gtk3: 命令找不到
eiskaltdcpp-gtk3: コマンドが見つかりません