The question is not relevant for English-speaking countries, or people who are English native speakers.
For the rest of the world, collecting data in their native language rather than in English is easier, as they will always be more proficient in their native language rather than in English, which they learnt at school, most of the time, and feel uncomfortable with, as they do not practise it on a daily basis.
However, collecting in one language only is a limitation. Most technological data are available in English only, as English became not only the language of trade, but the language of technology as well. And search engines are pretty stupid : if you type queries in English, you will have results in English. If you type queries in your native language, the results will be in your native language. But you will not get the same data, and you will not come up to the same vision through your analysis process. Language can, therefore, become a cognitive biasis.
As for me, I became proficient in English not only by learning them at school, but also by spending time in England, staying with English families, and avoiding French people while in England. This is one of the reason I avoid London, although I love the town : it sounds sometimes like the suburbs of Paris. I also spent some time working in England.
My mastery of English language allowed me first to become more proficient in Web searching, But last January, I was asked by one of my client, a school welcoming indian students, if I would be able to teach online reputation in English. Which, of course, I was. But, when preparing the lecture, I realised that teaching online reputation to non-French students meant finding non-French examples. And that the concept of online reputation was not perceived and managed the same way depending the country you are living in. Being aware of this culture difference, I had to think my lecture in a completely different way.
And this is the point of this day’s topic : to have a wider view on markets, people or situations, do not be afraid of leaving your native language behind you and think in English. The result will surprise you.
To end with this topic, and show how profitable a research in English can be, here are some fora in English, dedicated to web designers, which I found through queries in English :