I tried this with a Hello World project. After getting the content pipeline to export the font characters correctly (according to this page, it’s characters 1536 to 1791) I can see the text rendered left-to-right with no joining letters, like this:
The built-in text layout and rendering in MonoGame is really simple. It does not support RTL (though you can work around it), ligatures (to combine subsequent letters), proper kerning (only 1 kerning value per glyph is used) or even full Unicode (4-byte UTF-16 chars are not supported, e.g. emoji). There’s lots that needs to be improved, but it will take some time to implement it all due to the complexity
It’s definitely within the scope of MonoGame to support it all however.