Question: When I type any word ending with an 'l' (ell, like "local") and then press the `/` key, the 'l' is replaced with another symbol and the slash, '/', is omitted. How can I deactivate that function?

[![enter image description here](https://i.stack.imgur.com/lBxkj.gif)](https://i.stack.imgur.com/lBxkj.gif)

Answer: 
This looks like the behavior of some very old Mac fonts (Palatino was one of them) where you could make the character l with stroke (used in Polish and elsewhere) by typing such a sequence. Try changing your font. If this is in fact the cause of the problem, you should get rid of the font that does this, which should not be on any modern mac.
I had this same problem because I had an old Monaco font in ~/Library/Fonts/. I was able to disable the old font with FontBook, and the issue was resolved.

Note that I had the same issue with a number of leftover old fonts. I was able to clean them all out in FontBook with "Look for enabled duplicates..."