For the content, you want it to be clear, indicating your details as well as your friend's details.
Supporting documents (e.g. evidence of your passport/ID, address and any other items you mention) should be provided too.
Visaguide.World has a series of tips on this, as well as a couple of example letters.
It's important to note that you need to use their full name, details, and specifically their travel dates as well, so that you're all on the same page. If you use different dates to your guest's application, for example, it may cause some issues.
Finally, it might be worth contacting an Israeli consulate to clarify if they'll want anything else (eg do copies of ID etc need to be notarised).
As for Hebrew/English, maybe consider including it in both, if unsure. It's generally better to have too much documentation, than too little.