It started with Yochanan (Hebrew) -> Ioannis (Greek) -> Johannes (Mediaeval Latin) -> Jon (Middle English), but now every language seems to have a version, e.g.
- Hans
- Joanna
- Hanna
- Jan
- Ivan/Ivanka
- Vanja
- Jens
- Sean/Shaun/Shawn/Shane
- Joan/Jane/Jean/Janis
- Evan/Ewan
- Jock/Jack
- Ian/Iain/Ianto
- Juan
- Yiannis/Gianna
- Gianni/Giovanni/Vanni/Giovanna
- Jonas
- Ivo/Iva
- Eoin/Owen
- Seonaid/Siubhan
and those are just the ones I’ve heard used, there are hundreds more!
Jacob is similar. It is derived from an old Hebrew names and there are a ton of variants (including James and Diego)