Hi Brigui Mezri, thanks for your suggestion.
By default, after choosing fonts in GemPages Editor, we will generate Google Fonts link from the chosen fonts then link them to your theme.
But the current font manager has some limitations, one of them is that it will take at least 3 steps to use a custom font (fonts that not in the fonts list in GemPages Font Manager). So we have planned to bring you the ability to find and select the font that you want to use from Google Fonts. We will start working on it from the middle of July this year, tell me if you have any other ideas so we could make it better.