I left the Netherlands in 1994 and have since then worked in international environments where English is the business language. And business English is different from regular English: it has a very small vocabulary. Why? Many non-native speakers have to speak it, and you actually do not need a very rich vocabulary to get the basic business concepts across.

Now and then I come across business communications from the Netherlands and am surprised to see how the English language is invading the Dutch business language as well. I am not a big fan. You either write in English, or in Dutch. While I would not go as far as the French and insist on inventing new native words for English concepts (Internet browser?), I think it is a bit strange to see a Dutch sentence with 25% English words in it. Even if you did not intend to, the English words contribute to a feel of fluffy buzzword abuse.

For a presentation, the safest solution is to write the document in 100% English, so you can use it for every audience and change the language in which you present depending on your audience.