Since this has tuned out to become another language thread , my usual pinch of salt on the wound :
Mister slot :
Despite it being legal, multi-lingual R/T is simply dangerous and has cost lives. .
The problem with multi lingual R/T is just the opposite : it is not dangerous and has not cost many lives as you say. If it had, then it would be easy to argue in the ICAO council everytime the subject comes on the table.
Even States that did not have it, had to implement it on this very argument ( e.g Canada)
Sonnendec :
I really admire your courrage here .
Just a friendly correction when you said :
The german controller is applying the international rules, since german is NOT an ICAO language. Spanish controllers are applying the international rules because spanish IS an ICAO language and the pilots have the right to be cleared in spanish.
The fact to be an ICAO language or not has nothing to do with this. The legal basis to use national language on the R/T is an ICAO convention article which says that the language to be used on the R/T is the language of the Country overflown , and in absence of agreement, English shall be used or made available (i.e though an interpreter ).
Every State can use his national language in addition to English. Most do.
And for info Germany uses German on the R/T at its regional airports .