Unexpected languages

[ReneZ]

Hello Zhe (I hope that's right),

many thanks for your feedback. My problem is certainly that I only have some superficial knowledge of modern Mandarin (I was about HSK-1 level but have forgotten much).
Clearly, it would be important to know what the language looked like in the 15th century, and I have not been able to find anything.
I am assuming that Cantonese and Mandarin derive from a common ancestor, but even this I could not find, let alone when this was.
I also heard that the tones were introduced at some point in the past, and I have no information how long ago that was.

I am almost fluent in Thai, and this language has had an alphabet since the 15th Century.
The syllable structure is not quite as consistent as Chinese.
It has more words consisting of one syllable, and also composites of two or more.
In addition, it has numerous words which consist of two syllables that cannot stand alone. (They don't mean anything by themselves).
It also has syllables that are 'closed', i.e. ending with a 'stop' consonant, similar to Cantonese. Finally, it borrows heavily from Sanskrit, which introduces longer words, though these do not appear much in common speech.