1. It is scientifically correct to assume that the English language has socalled “mixed character”?

12. What is the principal difference between unassimilated and assimilated borrowings? The degree of assimilation.
Unassimilated words differ from assimilated ones in their pronunciation, spelling, semantic structure, frequency and sphere of application. However, there is no distinct border-line between the two groups. There are also words assimilated in some respects and unassimilated in others, they may be called partially assimilated. Such are communiqué, détente not yet assimilated phonetically, phenomenon (pl. phenomena), graffito (pl. graffiti) unassimilated grammatically, etc. So far no linguist has been able to suggest more or less comprehensive criteria for determining the degree of assimilation of borrowings.
The degree of assimilation depends in the first place upon the time of borrowing. The general principle is: the older the borrowing, the more thoroughly it tends to follow normal English habits of accentuation, pronunciation, etc.
However mere age is not the sole factor. Not only borrowings long in use, but also those of recent date may be completely made over to conform to English patterns if they are widely and popularly employed. Words that are rarely used in everyday speech, that are known to a small group of people retain their foreign -peculiarities. Если коротко то: The degree of assimilation depends on the time of borrowing, the extent to which the word is used in the language and the way of borrowing.