Maybe what you said is true. But China is a big country and I
believe there are still pockets of dialect speaking people there
who can communicate dialects in their pure forms.
The Teochew I heard from these two China students was indeed in
its pure form - not diluted with Mandarin. I know because
I wasn't eavesdropping but with them and
heard them spoke Teochew among themselves for a long
time in its pure form - a rarity I never encounter for a long
time.
I believe you heard they are pure. When you said they are not
diluted with Mandarin I hope you are not referring just to the
sounds only.
But still I have to say, China is a big country, but sadly the
Teochew speaking area itself is an extremely small plot of land
compared to the whole of China. (consisting of the 4
varieties: http://www.sgforums.com/forums/3545/topics/420371#post_10129387)
So the number of speakers is not as many as we may think.
I hope the two China students are not only pure in their
pronunciation (which we can discern easily), but hope they
are also pure in their underlying grammatical structure.
If the Chaozhou kids below 12 years of age are already speaking
a Mandarin grammar influenced Teochew, the next generation of
Chaozhou people will mark the end of the pure Teochew
generation.
There might be pockets of dialects that are still pure, but
sadly, these pockets left are made up of old people speaking them.
(which is the case happening to the Xuanzhou dialect in the
Anhui province)
(Xuanzhou dialect is classified as endangered dialect already,
if also nothing is done to Teochew, it will meet with
the same fate)
..........................................................................................
added: current state of Xuanzhou dialect (from
web)
http://zh.wikipedia.org/zh-sg/%E5%A4%AA%E9%AB%98%E5%B0%8F%E7%89%87
under "方言现状"
。。。宣州吴语受到官话(<<meaning
"Mandarin")严重侵蚀。。。
。。。或限于老人妇女应用。。。
。。。中年人尚能听懂老派土语(<<meaning
"Local Dialect")，但已讲不地道；年青一代则只能听懂零星土语，更谈不上说土语。。。
。。。男人已说市区官话，土话被认为妇女话。。。
。。。加上普通话的强势影响，吴语宣州片极有可能被官话完全融合、同化。。。
