ASCII-like unicode characters in chat

minecraft-java-edition

Occasionally (i.e., about 10-20 times in the last 1.5 years) I see players joining the server who appear to be using non-standard characters in their messages. I've been trying to identify the method those players are using, but I haven't managed to find any real lead.

Chat screenshot As you can see I am using standard unicode display for chat messages. Chat logs display the message as [LSL] JTheStr95: ????????? ??? ?????????.

They are answering questions rather quickly using this font, I have therefore eliminated the possibility of copy/pasting every character from a list.
About a year ago I was able to verify that everyone using these characters (over the course of multiple months) was sending messages with the same set of characters. Creating a custom keyboard layout with such Unicode characters shouldn't be too difficult, but I don't think it explains the fact that so many independent players use the same character set without any variation.
I have tried searching the Unicode tables to identify the symbols - especially the unusually long underscore - but I have been unable to find the exact characters.
It also appears to be toggleable - some of the players immediately returned to normal ASCII characters after being requested to stop it.

I am a member of a Spigot server, but this has (once) happened on an unmodified server as well.
Are there any known ways to reproduce this behavior?

They appear to be using ｆｕｌｌｗｉｄｔｈｕｎｉｃｏｄｅｃｈａｒａｃｔｅｒｓ．These are intended for when latin characters need to be used together with Chinese/Japanese/Korean characters, since they match the spacing of other glyphs. Keyboard drivers in these countries can often produce fullwidth Unicode characters directly.

There's several generators for these online, for example: