How can I get a LINGALA font?

pierrot34 wrote:

I need to write a book in Lingala, a DR Congolese language; thus I need to have Lingala font, which has some specificities

What specificities exactly? Are you referring to ɔ and ɛ? Many ordinary Latin fonts will have these already, so you won't need a special font for them.

You might want a special keyboard, although the ABC Extended input source provided by Apple can make those two characters without problem.