The business of languages and ICAO is often misunderstood and there are some interesting vatiations on the theme in this thread.
For the record, this is what ICAO says on the subject of language to be used in voice RTF communications (ref Annex 10, Vol 2, paragraph 5.2.1)
5.2.1 General
5.2.1.1 PANS.— When a controller or pilot communicates via voice, the response should be via voice. Except as provided by 8.2.12.1, when a controller or pilot communicates via CPDLC, the response should be via CPDLC.
5.2.1.2 Language to be used
5.2.1.2.1 The air-ground radiotelephony communications shall be conducted in the language normally used by the station on the ground or in the English language.
Note 1.— The language normally used by the station on the ground may not necessarily be the language of the State in which it is located. A common language may be agreed upon regionally as a requirement for stations on the ground in that region.
Note 2.— The level of language proficiency required for aeronautical radiotelephony communications is specified in the Appendix to Annex 1.
5.2.1.2.2 The English language shall be available, on request from any aircraft station, at all stations on the ground serving designated airports and routes used by international air services.
5.2.1.2.3 The languages available at a given station on the ground shall form part of the Aeronautical Information Publications and other published aeronautical information concerning such facilities.
5.2.1.3 Word spelling in radiotelephony. When proper names, service abbreviations and words of which the spelling is doubtful are spelled out in radiotelephony the alphabet in Figure 5-1 shall be used.
There are plans to change this but, for the moment, those are the International rules.
I know it doesn't help the thread much but I hope it can do away with some of the misunderstandings about what ICAO says - in particular, the business about Chinese etc. being an official language. It may be for ICAO documents but it ain't for RT!