Yabasic

[bprlhe]

Could re-use FreeBASIC lexer. Please add extension .yab to be detected as FreeBASIC. Thanks.

[JairoMartinezA]

Maybe you only need to add the desired extension in:

Options -> Lexers -> Lexer Properties

General Tab in File Types textbox:

Of course using one file with the desired lexer.

[Alexey-T]

https://wiki.freepascal.org/CudaText#File_types_config must be enough.