This UTF-8 line will not work in the properties files,
some.dutch.text = Één van de wijken van Curaçao heet Saliña.
It will incorrectly output to screen and look something like this,
�én van de wijken van Curaçao heet Saliña.
In Java code then you need to convert using Java's native2ascii tool,
The standard approach uses the ResourceBundle API in combination with properties files which contains externalized text. The ResourceBundle API will load the proper text based on the current Locale and the default (fallback) locale.
The problem is that at the bottom layer, the ResourceBundle API uses Properties#load(InputStream) method to load the properties files. This method uses by default the ISO-8859-1 encoding. This is explicitly mentioned in its javadoc as well,
The load(InputStream) / store(OutputStream, String) methods work the same way as the load(Reader)/store(Writer, String) pair, except the input/output stream is encoded in ISO 8859-1 character encoding. Characters that cannot be directly represented in this encoding can be written using Unicode escapes ; only a single 'u' character is allowed in an escape sequence. The native2ascii tool can be used to convert property files to and from other character encodings.