i2cdetect: 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 CentOS possible default full paths are:

/usr/sbin/i2cdetect - from package: i2c-tools

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/i2cdetect - from package: i2c-tools

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

Error in other languages:
i2cdetect: bevel nie gevind nie
i2cdetect: comandă negăsită
i2cdetect: comando não encontrado
i2cdetect: commande introuvable
i2cdetect: command not found
i2cdetect: käsku ei ole
i2cdetect: không tìm thấy lệnh
i2cdetect: komanda nerasta
i2cdetect: Kommando nicht gefunden.
i2cdetect: kommandot finns inte
i2cdetect: komut yok
i2cdetect: nie znaleziono polecenia
i2cdetect: níor aimsíodh an t-ordú
i2cdetect: no se encontró la orden
i2cdetect: no s'ha trobat l'ordre
i2cdetect: opdracht niet gevonden
i2cdetect: parancs nem található
i2cdetect: perintah tidak ditemukan
i2cdetect: príkaz nenájdený
i2cdetect: příkaz nenalezen
i2cdetect: команда не найдена
i2cdetect: командата не е открита
i2cdetect: 命令找不到
i2cdetect: コマンドが見つかりません