Throughout history there always seems to have been a predominant language for communication. Greek once served this role in the ancient Mediterranean until it was displaced by Latin, which was the language of the expanding Roman Empire. Latin then held sway throughout Europe until the Renaissance when the growing power and enviable culture of France made French the language of the ambitious. This was followed by English, which is now the default language of international commerce and science, not because it is any better than other languages but due to a combination of historical factors because of which Great Britain and the United States had a dominant presence on the world stage.
Currently, English has become the primary language for scientific communication at a global level. Moreover, for researchers, it has become a necessity to have publications in high impact factor journals. So, for non-native speakers of English, it has become increasingly important to have awareness of the English language and improve their understanding of it. For a non-native speaker of English, giving a convincing presentation in a language other than his/her own is very difficult, but there is no reason why this should prevent an effective presentation. Often, native English speakers give bad presentations because they end up talking endlessly in their presentation and are not able to convey the idea they intend to convey through the presentation; however, many non-native speakers give outstanding presentations as they have focused approach to convey their idea.
Nowadays, with the technology and software at hand, researchers are able to convey data in a very clear and objective manner, which is particularly helpful if you have a limited grasp of English. Moreover, by having sufficient presentable data for a presentation, research has to focus on using simple, clear language that conveys their interpretation of the results well. In fact, for the audience, the necessity is of a well-organized, rehearsed presentation with a clear, simple language.
To conclude, as a researcher, your primary focus should be on conveying the idea and the supporting data in a direct manner. Although not being comfortable with English can be a hindrance, your audience will always appreciate the idea that you have conveyed and will approach you if they have any questions. If you as the presenter have not been able to convey your research, the manner in which your conducted the presentation will not matter to the audience.