I am not very clearly about your scenario, it looks you implement a Multiraster which inherit from our Rasterlayer or RasterSource, then you call the ReadFieldAsDouble from the class GeoDBF, right?
For GeoDBF.cs, it looks the only enhancement is if the column type equal Numeric, Float and DoubleInBinary, the decimal-point will be replaced to cultureInfo.NumberFormat.NumberDecimalSeparator, so it should works better for your current culture.
If you want to keep the original behavior please set your target culture to CultureInfo of GeoDbf class, and make sure don’t call this API after that: internal void Open(FileMode fileMode, FileAccess fileAccess)