Your observations on English as an "interlanguage" is interesting. I can see this happening.
As to the observation of different Chinese dialects using English as an interlanguage within China (...I assume you didn't mean within China)...this is probably very rare. In my 9 years of living in China mingling with all sorts of regional and ethnic groups, I have never once seen this happen.
English as an interlanguage among Chinese people has become much rarer since the retrocession of Hong Kong strongly promoted the use of Mandarin there. Most of the examples I had in mind date from the era when an educated Hong Konger would be much more likely to speak English well than to speak Mandarin at all.
As to the observation of different Chinese dialects using English as an interlanguage within China (...I assume you didn't mean within China)...this is probably very rare. In my 9 years of living in China mingling with all sorts of regional and ethnic groups, I have never once seen this happen.