I don't believe you can do this on a computer, but I can show you how to do it on a phone or tablet.

Hold down on the letter you want to have an accent. There will be two hovering versions of that letter (with an accent):

Slide your finger along until the accent you want is highlighted:

Move your finger away from the screen:
WALLA! Ğ

This was a request from MoonycatTheWarrior