🗺 Geocode Google Spreadsheet Cells which uses OSM Nominatim.

geocode.js

function geocodeSelectedCells() {
  var sheet = SpreadsheetApp.getActiveSheet();
  var cells = sheet.getActiveRange();

  if (cells.getNumColumns() != 4) {
    Logger.log("Must select the Street, City, Lat and Lng columns.");
    return;
  }

  var streetColumn = 1;
  var cityColumn = 2;

  var latColumn = cityColumn + 1;
  var lngColumn = cityColumn + 2;

  for (var addressRow = 1; addressRow <= cells.getNumRows(); addressRow += 1) {
    street = cells.getCell(addressRow, streetColumn).getValue();
    city = cells.getCell(addressRow, cityColumn).getValue();

    address = street.replace(/ /g, '+') + ',' + city.replace(/ /g, '+');

    var response = UrlFetchApp.fetch('https://nominatim.openstreetmap.org/search/?q=' + address + '&format=json&addressdetails=1&limit=1');
    var json = response.getContentText();
    var data = JSON.parse(json);

    var lat = data[0].lat.replace('.', ',');
    var lng = data[0].lon.replace('.', ',');

    cells.getCell(addressRow, latColumn).setValue(lat);
    cells.getCell(addressRow, lngColumn).setValue(lng);
  }
}

function onOpen() {
  var sheet = SpreadsheetApp.getActiveSpreadsheet();
  var entries = [
    {
      name: "Find Lat/Lng",
      functionName: "geocodeSelectedCells"
    }
  ];
  sheet.addMenu("Geocode", entries);
};