Change a letter - a character - a glyph - in a font with Fontforge on Windows

HOW TO CHANGE A LETTER IN A FONT WITH FONTFORGE ON WINDOWS
(for dummies !)

I could not find a video about this so I made one myself.

You would like to have a font which distinguishes clearly 1, l, I, 0 etc.
There are already 3 fonts which offer this :
GO, ATKINSON HYPERLEGIBLE AND FINLANDICA
You will find the links below

But you still want to change a font on Windows so it has a slashed zero 0, a small l with a curve and a capital I with two serifs.

This we can do with Fontforge. But the demonstration will be done with fonts with an Apache 2.0 license, Roberto Sans and Roboto.
You could also alter a system font, but you would need to give it another name, use it only on your computer, which would be contrary to the license, and you could not embed your changed font in a pdf. Fonts with Apache 2.0 or SIL Open Font license however will allow you to do this.

Download Fontforge :
https://fontforge.org/en-US/
To install, you need administrator rights.

Download Roberto Sans by adding these two sentences for the URL :
https://www.1001fonts.com/
roberto-sans-font.html

Download Roboto with Apache 2.0 licence :
https://fonts.google.com/specimen/Roboto
Above at the right you can click "Download family"

A lot of Google fonts have permissive licences :
https://fonts.google.com/attribution
Use CTRL + F to search for apache

We will take the regular .ttf from Roberto Sans and from Roboto, and put these on the desktop, next to the shortcut of Fontforge.
First we drag Roboto-regular.ttf to the Fontforge shortcut ; now we draw a slash through the zero :
Double click on the slash / to open it.
Use the keys CTRL+A to select the sign
Use the keys CTRL+C to copy it
Close the sign
Now double click on the zero : 0
Use the keys CTRL+V to paste the slash /
Make sure it fits by dragging its points into the zero.

If it's perfect, use the keys CTRL+A to select both glyphs

Use the keys CTRL+SHIFT+O to eliminate the overlap.

Now we want to add 2 serifs on the capital i.
In Fontforge you click on the icon of a rectangle on the left. Edit and Undo will undo any mistakes.
You click on the icon of an arrow on the left to adjust your serifs.
Use the keys CTRL + A to select everything, and
CTRL + SHIFT + O to remove the overlap.
To make things easy, we will steal the small l with a curve from Roberto Sans and paste it in Roboto.
For this we need the regular .ttf from Roberto Sans
Now we give a new name to the changed Roboto font with the keys CTRL+ SHIFT+ F
Both in PS Names and in TTF Names you will need to change it.
Apache allows you to take a license on the glyphs you changed yourself, but the unchanged glyphs need to stay under Apache 2.0 license.
Thus it is logical for your new font name to stay under Apache.

If you want to distribute your own font, a text notice should be added, saying you used Roboto and you changed the zero, the small l and the capital I. In addition you should add a text file with the Apache 2.0 license.
While giving your font to a friend or embedding it in a pdf is legal, I would advise you to seek judicial advice if you want to sell your font.
However, if you alter a font under the SIL Open Font Licence 1.1 you are obliged to keep your new font under the same license, and - contrary to Apache - you are not allowed to sell the font by itself.
Add the 2 sentences to see the URL of the SIL OFL
https://scripts.sil.org/cms/scripts/
page.php?item_id=OFL-FAQ_web
.
Use the keys CTRL+SHIFT+G to generate the new font. Do not save it as a Postscript PS font, but as Truetype. If it was Open Type, save as Open Type (CFF).

The 3 fonts which are highly legible :

GO from Bigelow & Holmes .Download :
https://www.fontsquirrel.com/fonts/go

ATKINSON HYPERLEGIBLE
https://brailleinstitute.org/freefont
In the download you'll find the text of the SIL Open Font License 1.1, as OFL.
FINLANDICA, the official Finnish typeface which is equally under SIL OFL 1.1 license.
Add the 2 sentences for the URL :
https://fonts.google.com/specimen
/Finlandica

Addon "High Contrast" for Google and Edge will make the text on a website have more contrast.
Addon "Dark background and light text" for Mozilla Firefox does the same.
To have larger text on a website: CTRL and +
to have smaller text: CTRL and -
to return to original : CTRL and zero 0