It should work in both cases, but it's recommended to use utf-8 with bom. When there is no bom, you can never know if it is utf-8 or not.
But you can still open this xml in excel (or other comfortable xml editor), edit all string and then save it cack from excel to xml. Encoding will be saved ok because of excel processing. There is no need to edit xml in any text editor. It is yor choice.
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