... if you want to let me know your native language so I can include you.
... if you know the native langauge of a member who is not listed here.
Why Is a List of Native Speakers Important?
Knowing who the native speakers are will help you find trustworthy sentences that you can translate into your own native language.
Of course, native speakers sometimes make mistakes, too, but their mistakes are usually typing mistakes.
Non-native speakers aren't just more likely to make grammar and vocabulary mistakes, but also often create sentences that aren't the most natural way things would be said.
Who Is Included?
These are all the native speakers I know about, either from what was written in their profiles or what I've been told. I have used this information under the (perhaps false) assumption that Tatoeba Project members are honest.
I have limited this to one native language per member. I know that there are some members that perhaps grew up speaking more than one language, but even for those people, one language is usually stronger. For most people, it's the language in which they did their formal education, have read the most, written the most, watched the most TV, listened to the most radio, and had the most conversations.