My translation keep showing “Translation is unavailable at the moment. Try again at a later time”.

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

Follow the advise from my old friend @Old Toad - First.

If still having issues - Does the computer have any Safari Extensions installed that would interfere with this process ?

In my case the Ads and Stuff Blocker does not but not all Ad Blockers are not the same

Is there any Third Party Security Software installed and used on this machine ?

Follow articles from Apple on Translation Services

refer below

Webpage Translation in Safari on Mac

Translate a webpage in Safari on Mac

Then a question for the User

Is this information accurate iMac 24″, macOS 13.2 ?

Current version Ventura 13.5.1 is available and may or may not apply to this issue

refer below

Keep your Mac up to date

Apple security releases

Welcome