Steps to reproduce:
1. Switch "enable-query" to true, "online-mode" to false
2. Start the server.
3. Log in under some non-ASCII name, for example "игрок" (non-official launcher).
4. Connect to server, it will handle your name correctly as any other utf-8 name.
5. Query the server, for example, with PHP-Source-Query (https://github.com/xPaw/PHP-Source-Query).
6. Discover that instead "игрок" server query says that there is a player with some strange nick like "B3J@U".
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Expected output:
Server query returns "игрок"
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Real output:
Server query returns "B3J@U"
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Explanation:
There is a class net.minecraft.server.v1_8_R3.RemoteStatusListener. A method "private byte[] b(DatagramPacket var1)" is responsible for forming return string for query. There are strings "
for(String p: this.b.getPlayers())

", responsible for forming player list. "this.v.a(String str)" leads to "this.stream.writeBytes(b);" what leads to function contains "out.write((byte)s.charAt)". But not all chars can be converted to byte without losses! Some, non-ASCII, are losing senior bits what leads to unrecoverable data loss.
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Fix:
Replace "this.v.a(p);" to "this.v.a(p.getBytes(Charset.forName("UTF-8")));this.v.a("");" in net.minecraft.server.v1_8_R3.RemoteStatusListener class.
After that RemoteStatusListener handles utf-8 players' names correctly. Tested, works.
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It is expected that new patch will be added to the SPIGOT project.