May I ask a question about plugin writing: Objective-C language is only used to generate xib files. If my plugin does not require dialog functionality, I do not need to use Objective-C language, right

May I ask a question about plugin writing: Objective-C language is only used to generate xib files. If my plugin does not require dialog functionality, I do not need to use Objective-C language, right

Objective-C is not used for XIB files. Instead, the application Xcode is used to edit XIB files and convert them to NIB files.

You can write plugins with different programming languages. The more common to write plugins in Glyphs are Python and ObjectiveC. You can pick the one you are more comfortable with. ObjectiveC can be a bit better to optimize for performance. But as a beginner, Python is much easier to learn.

Then there are several ways to build a user interface. One are the .xib/.nib files and another option is to use the vanilla module. There are examples in the GlyphsSDK repo. Please have a look at the readme files in each folder (e.g. GlyphsSDK/Python Templates at Glyphs3 · schriftgestalt/GlyphsSDK · GitHub)

thanks very much! but how is. xib written?

The .xib is a documents that you can edit in Xcode.