Hello OlivierMyre,
Thank you for using Apple Support Communities.
I see that you are wanting to view fonts without having to open Font Book when you want to change fonts. If you enable specific fonts in Font Book, you should then be able to see and change to those fonts from within the application. See the following:
In situations where you'd like to prevent a font from being available in applications, but you don't want to completely remove the font from your Mac, you can use Font Book to disable the font.
- In Font Book, click "All Fonts" in the Collection column.
- Click the name of the font in the Font column.
- Choose Disable "Font Name" Family from the Edit menu.
Fonts that have been disabled have their names displayed in gray text with the word "Off" appearing next to the font's name.
System fonts can't be disabled.
If you'd like to enable a font that was previously disabled, click the name of the font from the Fonts column, then choose Enable "Font Name" Family from the Edit menu.

You can also disable or enable all fonts in a collection: Click the name of the collection in the Collection column, then choose Disable "Collection Name" or EnableCollection Name" " from the Edit menu.
Mac Basics: Font Book
Once this has been done, you should then see the fonts in the associated menu in whatever application you are using.
Best regards.