lang strings: minor fix

[vieridipaola]

Hi,

Minor fix:

# grep -i -r "sent dtmf" ./lang/*
./lang/de.json:    "send_dtmf" : "Sent DTMF",
./lang/en.json:    "send_dtmf" : "Sent DTMF",

The en.json string should be changed to "Send DTMF".

The de.json string should be changed to "DTMF senden".

Thanks