If we take examples from other countries, it is obvious that BOTH languages are required, especially in the field of medicine.
My physician colleague from China is a good example. He speaks Cantonese very well and Mandarin just so-so. He did his medical school training in North America and is a professor now. So why does he give lectures in English only when he visits China? He says it is because he learned medical terminology in English only and is not familiar with the exact equivalents in Mandarin. The conference organizers in China ALWAYS have to have a translator for his talks.....because, of course, the local doctors in China do not know English very well and are not familiar with medical terminology in English. Importantly, we also need to remember that the Mandarin-speaking patient population in China is unlikely to know English at all. They need a doctor speaking to them in their local language and using local language for medical and scientific terms.
This example applies to all countries.....so, of course, both English and Estonian for science and medicine in Estonia.

Vocabulary, in any language can be developed.
Decades ago, computer terminology, for example, didn't exist; not in English, Estonian, Zulu or Apache. Yet, it evolved, somehow, in many languages.
Professor Smartypants Niitsoo should examine that phenomenon before he tells the rest of the world what to do. Academics are a tedious bunch.
Kes oskab, teeb. Kes ei oska, õpetab.

Let's have a look at Prof. Niitsoo's English, to see if it's comprehensible to native speakers.
That of many of his colleagues certainly isn't, even though they'd arrogantly beg to differ.

When Israel ceases to be a nation-state and abandons Hebrew and Yiddish languages -- only then should Estonia start debate about following suit.

It would be tempting to dismiss young Dr. Niitsoo's comments as facile, irreverent or immature. He seems to be a bit of a child prodigy, but with perfectly commendable credentials, rooted in linguistics and developed in IT. We need to identify exactly what he is saying. He is not advocating the devaluation of the Estonian language, but simply commenting on the hurdles academics have in translating their work between English, the language of international academia, and Estonian, the language of the people of Estonia. Many necessary terms lack appropriate equivalents in both languages, and effort is required to round out the vocabulary, -- effort that I suspect Niitsoo would prefer to have devoted to the academic task. This is an unfortunate consequence, but a necessary one. Academics need advanced capability in multiple languages. Even the Russian-speaking ones in Estonia need to develop proficiency in the language of the land.