Hi,
We rely on Java properties file support, and the encoding of .properties files is assumed to be ISO-8859-1 with JRE < 9. The safest way is to convert your text containing non ascii characters using the native2ascii tool:
https://native2ascii.net/
For example, Rubén España should be written Rub\u00e9n Espa\u00f1a
Another option is to try using JRE 9 or greater, since it will first try to open the .properties file as UTF-8.