solved!
Root cause was that I designed a flow AND creating the data table. this had nothing to do with international settings 😞
The table generated was creating, for the numeric fields, a 'floating point number' field (sorry that my interface is italian but it's locked by my organization) with minimum value 0 and maximum 10.000.000.000:

this was blocking the import. instead, i deleted all these columns and replaced with 'decimal' fields:

and it worked! 🙂
Now, the question are:
- why the automatic table generator creates datatypes that are not working for the dataflow with arbitrary limits?
- why having this error message that made me losing one weekend and led to wrong path? I had to be really creative to find another root cause..
And as an old style (C++/Java) programmer, i still don't understand the difference between those two datatypes...
https://docs.microsoft.com/en-us/powerapps/maker/data-platform/types-of-fields#using-the-right-type-of-number
"When choosing the correct type of number column to use, the choice to use a Whole Number or Currency type should be straightforward. The choice between using Floating Point or Decimal numbers requires more thought.
Decimal numbers are stored in the database exactly as specified. Floating point numbers store an extremely close approximation of the value. Why choose extremely close approximation when you can have the exact value? The answer is that you get different system performance.
Use decimals when you need to provide reports that require very accurate calculations, or if you typically use queries that look for values that are equal or not equal to another value.
Use floating point numbers when you store data that represents fractions or values that you will typically query comparing to another value using greater than or less than operators. In most cases, the difference between decimal and float isn’t noticeable. Unless you require the most accurate possible calculations, floating point numbers should work for you."
Anyway, thanks for your help!