As the Tibetan language uses the same script as Dzongkha, it follows that providing support with WebFonts for one language means that you can support the other language as well.
What we do in general is when we assume such things, we enable support on translatewiki.net in anticipation of people who do know such things providing us with feed back.
When you know Tibetan, help us test the font. When you feel really happy with our efforts, you may even help us and localise the most used MediaWiki messages, the Babel extension as you can see needs some work as well. You may even join our language support team for Tibetan.