try this...
select convert(int,convert(float,replace('-6.353,35',',','')))
as there are (,) Commas it cannot be converted to float,so remove the (,)commas after converting to float we can convert to int
If you want decimal values, then you should use float
select convert(float,replace('-6.353,35',',',''))
Edit
Like @marc_s suggested, it is preferred to use decimal rather than float
select convert(decimal,replace('-6.353,35',',',''))
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