My mom always told me that kissing is dangerous because you can get a lot of diseases doing it. If I buy a condom, and ask him to put it in his tongue, will it reduce my changes of getting diseases?

While it is true that you can get some diseases from kissing, herpes, meningitis, and probably a couple other things as well; it just isn’t likely.  You could spend your life being scared of everything, but that’s no way to live.  Kissing is certainly not something you should be afraid of.  You can get some diseases just by being around people with them, but you’re not going to live as a hermit.

No one would ever wear a condom on their tongue, so don’t even suggest it.  Wear one if you have sex though.  I don’t even think that wearing a condom on a tongue would help in the least.  Not only that but it could be a choking hazard.

I think your mom is being extremely over cautious and telling you things that aren’t entirely true.  She’s probably worried that you may have sex too early, do her a favour and wait on that one, but she should not be denying you a simple kiss.