Interesting but still missing the point Oluf,
Communications is indeed a weak link in Safety. Often the weakest.
The problem is communications is more the use of a single phraseology that about a single language.
let's take a recent example in a country that do has English as official language : the USA :
the decision last year by ICAO to change taxi phraseology :
e.g . "taxi to holding position " ( was taxi to holing point before ) it is now conflicting with the US FAA phraseology "taxi into position and hold " meaning a totally different thing. ( in one instruction you taxi and hold BEFORE entering the runway and in the other you ENTER , line up and hold.)
The US , accoring ICAO , should use "line up and wait " but refuses to change its habbits on the account that : "15.000 controllers and 300.000 pilots in the US are not going to change for a few forgein pilots.."( in the Continental US 96% of the traffic is done by US aircraft. ) They argue that ICAO should change again their phraseology to make it less ambiguous with FAA.
Everyone ( ICAO and FAA) now awaits a serious incident or an accident to back off and return to sanity.
This is only one example, I can produce more, but you get the point I guess.
.
As our Canadian friend said, mixing languages on the R/T is annoying for some but it is not unsafe per se. But Applying bad phraseology might kill you one day.
Finally , AIRWAY, I do not think Chinese ( in singular ) is the most spoken language in the world . the official language in China is Mandarin and is , I am told, only spoken by the mainland elite and in Taiwan .
The vast majority of the people speak only their regional language , Cantonese being the largest I guess ( used in Hong Kong for instance ) But I migh be wrong .