Here is a screenshot of Civilization with a worker on a fully improved grassland tile (bottom middle).
Here is a screenshot of CivOne with fully improved grassland tiles, getting 1 extra trade on each.
The government is Democracy in both screenshots. According to the reference chart, "Railroads increase food and resource production in a map square by 1/2 (rounded down). They increase trade by the same amount, but before the effects of Republic or Democracy governments.", so the calculation adding trade should happen before the trade bonus from Republic or Democracy governments.
Here is a screenshot of Civilization with a worker on a fully improved grassland tile (bottom middle).
Here is a screenshot of CivOne with fully improved grassland tiles, getting 1 extra trade on each.
The government is Democracy in both screenshots. According to the reference chart, "Railroads increase food and resource production in a map square by 1/2 (rounded down). They increase trade by the same amount, but before the effects of Republic or Democracy governments.", so the calculation adding trade should happen before the trade bonus from Republic or Democracy governments.