I want to include keyboard symbols like those: ⌘ ⇧ ⌥ ⌃ ⌫ into the typeface I’m developing - because they are needed in the UI of the product where this typeface is customised for. But I haven’t found enough information regarding:
how should they react to the weight changes across the typeface?
where can I find a full list of those symbols that would include as many keyboards (Mac, PC, etc.) as possible? - they don’t seem to be included as a list in glyphs app.
I’ve figured most typefaces don’t have them included in the glyphs set - anyone knows why or why not?
It would be nice if someone with experience in this topic can share with me some best practices.
For Mac, you have already posted the most important ones: ⌘ ⇧ ⌥ ⌃. Some other commonly used symbols are ︎ ⏎/ ⌫ ⌦ ⎋ ⌧ ⇪ ⇟ ⇞. For Windows and Linux, these are also useful: ⊞ ⎇ ≣ ◆ ⎈. In general, arrows are used for many keys: → ← ↑ ↓ ⇥ ↹ ⤒ ↸ ⇱ etc.
There are many more at The Macintosh Biblioblog: Special Key Symbols, but most of them are rarely used. There is no consensus, which Unicode characters to use for certain keys. Return might be ⏎ or or ⤶ or ↵.
If a unified appearance of key symbols is important to you, you might need to offer a stylistic set that swaps conventional glyphs for keyboard-symbol glyphs.
For example, here I have decided that ⇪ should match ⇬ and ⇭, but there is an OpenType feature to turn /capslock into /capslock.alt:
︎ ⏎/
⌫ ⌦ ⎋ ⌧ 
⇪ ⇟ ⇞. For Windows and Linux, these are also useful: ⊞ ⎇ ≣ ◆ ⎈. In general, arrows are used for many keys: → ← ↑ ↓ 
⇥ ↹ ⤒ ↸ ⇱ etc.
