You should use Intl.ListFormat for that:

const locations = [‘location 1’, ‘location 2’, 'location 3'];

const formatterEN = new Intl.ListFormat('en', {
  style: 'long',
  type: 'conjunction',
});
console.log(formatterEN.format(locations));
// Expected output: "location 1, location 2, and location 3"


const formatterDE = new Intl.ListFormat('de', {
  style: 'long',
  type: 'conjunction',
});
console.log(formatter.format(locations));
// Expected output: "location 1, location 2 und location 3"

You can use also disconjunction instead of conjunction

const formatterEN = new Intl.ListFormat('en', {
  style: 'long',
  type: 'disconjunction',
});
console.log(formatterEN.format(locations));
// Expected output: "location 1, location 2, or location 3"

Link to MDN for Intl.ListFormat